NETWORK CONTROLLER FOR DIGITALLY CONTROLLING REMOTE DEVICES VIA A COMMON BUS

Abstract: The present invention provides a network controller that directs communications with a variety of remote devices via a common bus. The network controller includes a transmitter for transmitting messages via the common bus, and a receiver for receiving messages from the common bus. Additionally, the network controller includes a clock for providing clock signals to both the transmitter and receiver. The transmitter and receiver are selected such that the network controller is capable of selectively operating in either synchronous or asynchronous mode. In operation, the network controller is configured in either a Manchester encoding or a Universal Asynchronous Receiver Transmitter (UART) protocol. The transmitter transmits messages comprising a command and an address of at least one remote device. In one embodiment, the transmitter simultaneously transmits messages to a plurality of remote devices in accordance with a group address comprised of a multiple bits with each bit associated with a respective group.

Description: NETWORK CONTROLLER FOR DIGITALLY CONTROLLING REMOTE DEVICES VIA A COMMON BUS FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This invention was made with government support under Cooperative Agreement No. NCCW-0076 awarded by NASA. The government has certain rights in this invention. CROSS-REFERENCE TO RELATED APPLICATIONS The present application claims priority from U.S. Provisional P atent Applications S/N 60/254,137, entitled: NETWORK CONTROLLER FOR DIGITALLY CONTROLLING REMOTE DEVICES VIA A COMMON BUS filed on December 8, 2000, the contents of which are incorporated herein by reference. FIELD OF THE INVENTION The present invention relates generally to network controllers and, more particularly, to an apparatus and method for digitally directing communications with a variety of remote devices via a common bus. BACKGROUND OF THE INVENTION In many industries today, monitoring systems are used to assess either possible system failures or the affects of environment and other external forces on an object of interest. For example, in the avionics industry, monitoring systems are employed to monitor parameters, such as strains, acceleration, pressures, corrosion, and temperatures at various critical structural locations on aircraft. Similarly, such monitoring systems could be used in the automobile industry to control and monitor everything from on/off occupant controls to drive-train controls and multimedia systems. Many of these conventional monitoring systems use a plurality of remote devices, such as sensors, actuators and subsystems that are placed about the object being monitored at the critical locations. Many of these conventional monitoring systems utilize dedicated analog signal connecting, thus making the monitoring system dedicated to the application and complicating the wiring systems with separate wiring to each device to be monitored. Where networking exists there is often many multiplexer units networked together that gather many individual analog signals. While the analog wiring is now shorter, a significant amount of dedicated wiring to individual transducers still exists. Further, existing and proposed "smart transducer" protocols, which permit signal conditioning at the transducer and offer a fully digital networking solution without significant analog signal wiring, often lack time- determinism, speed, simplicity to achieve cost effectiveness inmost applications. J« In many industries today, including the avionics and automotive industries, the complexity of the network may make many conventional monitoring systems impractical for a number of reasons. Specifically, the dedicated wiring and signal conditioning can be expensive, bulky, heavy and hard to install and maintain. This is especially critical in aircraft applications, where weight concerns are at the forefront. Further, in the automotive industry, the added wiring may add to the weight and possibly the size of the car. In addition, dedicated wiring and signal conditioning renders automotive electronic-control modules application specific and thus more costly. Further, dedicated wiring limits the amount of factory and dealer available options available due to the extra cost of preparing an automotive platform for the options with extra harnessing and interfaces. Additionally, as stated, many conventional monitoring systems transmit data in an analog format. Typically, analog signals are susceptible to noise introduced into the signals during data transmission. Given that many of the transmitted signals have a low amplitude to start with, this noise can corrupt signals as they propagate from the transducer to the signal conditioner. Further, as many of these remote devices are scattered a fair distance from the controller, the electrical lines connecting the remote device to the controllermay be sufficiently long to cause signal degradation due to DC resistance. In light of this, it would be advantageous to replace the dedicated wiring and the analog transmission with a common bus and digital transmission of data. But, many conventional digital networks suffer from a variety of problems themselves. For example, many existing digital networks demand complicated protocols requiring processors and, thus, suffer from high overhead network communication. The use of processors in such systems results in bulky and more expensive network interfaces. Additional problems include low maximum bit rate, low effective data rate (due to overhead), expensive physical layers, and low network device count. Moreover, many computer systems that include digital networks do not operate in a time- deterministic manner. These computer systems generally lack the capability to schedule a trigger command to the network components that repeats with any precision timing . In light of the foregoing, it would be advantageous to provide a network system that allows network components to digitally communicate over an inexpensive, simple and high-speed, yet robust, network line with a simple message protocol, small component size and low wire count. The network system would also advantageously operate without the use of a microcontroller or processor for the network components. Also, the network system would support both acquisition and control, acquire data simultaneously from the components and operate with synchronized data samples from the components. Further, the network system would allow for high component counts, longer network lines and insure time-determinism in a precise manner. SUMMARY OF THE INVENTION In view of the foregoing background, the presentinvention therefore provides a network controller for digitally directing communications with a plurality of remote devices via a common bus. The network controller of the present invention allows various remote devices to communicate in either synchronous or asynchronous modes over an inexpensive, simple and high-speed, yet robust, network line with a simple network protocol, small component size and low wire count. Advantageously, the network controller of the present invention connects to the remote devices via a common network, thereby permitting the various remote devices to share the same wiring for communicating with the network controller. Additionally, the network controller of the present invention allows for high component counts, longer network lines, and insures time-determinism in a precise manner. The network controller also allows data to flow to and from the remote devices at an alterable bit rate, supports both acquisition and control, and acquires synchronized data simultaneously from the remote devices using either an optional continuously synchronous clock, or a synchronized state change during asynchronous communication (often referred to as "isochronous"). Further, the network controller operates in conjunction with a network protocol that allows the controller to communicate with either one or several remote devices at a time across the network. Importantly, the network protocol has a fixed, low-level instruction set. Due to the simplicity of the network protocol, the network controller of the present invention can operate with remote devices that lack a processor and, instead, comprise state machines that use pass through logic to process the commands and data between the network controller and the remote devices. As previously stated, the network controller of the present invention allows various remote devices to digitally communicate in either synchronous or asynchronous modes over an inexpensive, simple and high-speed, yet robust, common network. The network controller is capable of communicating with sensors, actuators and subsystems, thus allowing for both acquisition and control. The network controller also includes a transmitter for digitally transmitting messages via a common bus, and a receiver for receiving messages from the common bus. Additionally, the network controller contains a clock for providing clock signals to both the transmitter and receiver. The transmitter and receiver are selected such that the network controller is capable of selectively operating in either synchronous or asynchronous mode. In synchronous mode, the transmitter digitally transmits both the messages and clock signals via the common bus. And, in the asynchronous mode, the transmitter digitally transmits messages at a predetermined bit rate without any accompanying clock signals via the common bus. To further allow the network controller to receive synchronized data samples from the remote devices, in one embodiment, the network controller further includes a clock transmitter for transmitting the clock signals via the common bus. This clock signal is used by the remote devices in a synchronous mode to clock in and clock out data. In the asynchronous mode where the remote devices operate based on bit rate as opposed to a synchronous clock signal, the clock transmitter operates at a constant, null, level. In another embodiment, the network controller issues a baud select command that defines the predetermined bit rate at which the transmitter will transmit messages in the asynchronous mode. Additionally, in embodiments where the network controller operates in asynchronous mode, the receiver receives messages from the common bus based on the bit rate at which the messages are transmitted by the controller. Further, all of the remote devices can synchronize in a singular manner to a predetermined state-change bit within the message often referred to as isochronous mode. In yet another embodiment, the transmitter of the network controller is capable of altering the predetermined bit rate at which messages are transmitted, while communicating with the plurality of remote devices. In this embodiment, the receiver receives messages from the remote devices via the common bus at the same predetermined bit rate at which the network controller previously transmitted the messages to the remote devices. This makes the receiver capable of receiving messages as the transmitter alters the predetermined bit rate without relying upon any clock signals. In one embodiment, the network controller transmits an example message to the remote devices at an altered bit rate following alteration of the predetermined bit rate to insure the remote devices are in sync with the network controller. In a further embodiment, the network controller issues a baud select command to the transmitter that defines the predetermined bit rate at which the messages will be transmitted. As previously stated, in operation, the network controller works in conjunction with a network protocol having alow-level instruction set to allow the network controller to communicate with either one or several remote devices at a time across the network. Therefore, in various embodiments, the network protocol is configured in either a Manchester encoding or a Universal Asynchronous Receiver Transmitter (UART) protocol, depending upon the command protocol the remote devices are capable of understanding. In one embodiment, the network controller and the remote devices are preconfigured to operate either in the Manchester encoded form or in the UART encoded form. In another embodiment, the network controller receives a command protocol select command such that the subsequent configuration of the network controller is based upon the command protocol select command. In another embodiment, the network controller sends the protocol select command to the transmitter and receiver to identify the command protocol according to which the plurahty of remote devices are capable of communicating, and the transmitter and receiver thereafter transmit and receive messages, respectively, in accordance with the command protocol identified by the protocol select command. As stated above, the simplicity of the network protocol allows the network controller of the present invention to control remote devices that lack a processor and, instead, comprise state machines. Because the network controller controls various remote devices via a common bus and insures time-determinism in a precise manner, the network controller operates using an addressing scheme. In one embodiment, the transmitter transmits messages comprising a command and an address of atleast one remote device. Further, the transmitter simultaneously transmits messages to a plurality of remote devices in accordance with a command and an address representing a group of devices. In this embodiment, each remote device is capable of reacting and responding to an assigned unique address and/or one or more assigned group addresses. The group address transmission enables the transmitter to direct a message to a group of remote devices. In a further embodiment, the transmitter can additionally transmit messages to individual remote devices in accordance with a unique logical addresses assigned to each of the plurality of remote devices. In another embodiment, the transmitter is also adapted to transmit messages to all of the plurality of remote addresses in accordance with a global address. Once configured, the network controller can then transmit messages between itself and the remote devices according to the same command protocol with which the plurality of remote devices are capable of understanding. In embodiments wherein the network controller transmits messages based upon the Manchester encoding command protocol, the network controller transmits the messages in either synchronous or asynchronous mode. These messages, transmitted in the Manchester encoding command protocol, comprise a sync portion, a message body and a parity flag, with the value of each transmitted bit defined by a voltage transition between first and second states. In one embodiment wherein the network controller transmits messages in the synchronous mode and includes a clock transmitter, the network controller is capable of transmitting messages via the transmitter while concurrently transmitting a clock signal to the of remote devices via the clock transmitter. And, when operating in asynchronous mode, the network controller transmits messages at a predetermined bit rate without transmitting a clock signal. In embodiments where the network controller transmits messages accordmg to the UART command protocol, the network controller transmits the messages at a predetermined bit rate and according to a non-return-to-zero (NRZ) bit format. In another embodiment, also where the network controller transmits messages according to the UART command protocol, the network controller transmits an idle pattern to reset the plurality of remote devices prior to transmitting each message. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block diagram of an electrical network system implementing one embodiment of the network controller of the present invention; FIG. 2 is a schematic block diagram of the network controller accord ing to one embodiment of the present invention; FIG. 3 is a block diagram illustrating the operational steps of the network controller during operation of a device inventory word search according to one embodiment of the present invention; FIG. 4 is a block diagram illustrating the operational steps of the remote device during operation of a device inventory word search according to one embodiment of the present invention; FIG. 5 is a schematic diagram of an electrical network system implemented on an aircraft; and FIG. 6 is a schematic diagram of a translation device implemented with an electrical network system, such as that illustrated in FIG. 5. DETAILED DESCRIPTION OF THE INVENTION The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. As described above, many conventional analog network systems require separate sets of dedicated wires and signal conditioners to run from each component within the system, which can be expensive, bulky, heavy, hard to install and maintain, and suffer from signal degradation due to DC resistance of the wires and noise. Additionally, many conventional digital network systems demand complicated communication schemes requiring processors and, thus, suffer from high overhead network communication. These conventional digital network systems may also require separate clock signals, may not support both acquisition and control, and may only support short network lengths. Moreover, many conventional digital network systems do not operate in a time-deterministic manner and have bulky network interfaces, slow network data rates and a low network device count. As described in greater detail below, the present invention remedies these and other problems by providing a digital network system that allows various remote devices, such as sensors, actuators and subsystems, to communicate over an inexpensive, simple and high-speed, yet robust, network line with a simple message protocol, small component size and low wire count. Advantageously, the network controller of the present invention connects to the remote devices via a common network, thereby permitting the various remote devices to share the same wiring for communicating with the network controller. Additionally, the network controller of the present invention allows for minimally sized devices, longer network lines, and insures time-determinism in a precise manner. The network controller also supports both acquisition and control, acquires data simultaneously from the remote devices and operates with synchronized data samples from the remote devices. Further, the network controller of the present invention operates in conjunction with a network protocol that allows the controller to communicate with either one or several remote devices at a time across the network. Importantly, the network protocol used by the network controller has a fixed, low-level instruction set. Due to the simplicity of the network protocol, the network controller of the present invention can operate with remote devices that lack a processor and, instead, comprise a state machine that use pass through logic to process the commands and data between the network controller and the remote devices. As mentioned above, the network controller of the present invention is used to interconnect various remote devices via a common network bus. FIG. 1 is an illustration of one embodiment of the implementation of the network controller of the present invention. This illustration is provided so that a more complete understanding of the present invention may be appreciated. It must be understood that the present invention is not limited to this configuration and may be embodied in many different network systems. With regard to FIG. 1, a general embodiment of a networked system 25 in which the present invention is used is shown. Specifically, the networked system includes a host computer 30 such as high-level processor or personal computer that processes data from and sends commands and data to remote devices 36, such as sensors, actuators and subsystems, located at desired points in the network. The networked system further includes the network controller 32 of the present invention connected between the host computer and a network bus 34. Importantly, the network controller of the present invention comprises a part of a digital network that also comprises a common bus interconnecting the network controller and remote devices. In some embodiments, the remote device 36 may include a network device interface (NDI), not illustrated, connected to the network 25. The NDI is used in embodiments in which transducers, whether sensors or actuators, cannot communicate directly with the network controller. The NDI receives and interprets commands from the network controller and controls signal conditioning, such as receiving data from sensors or activating actuators, based on the commands and data from the network controller. The NDI further includes a block of stack memory for storing the data and/or messages from the sensors and/or actuators. In this embodiment, the network controller is capable of pushing data on or popping data off of the top the stack memory. Also, the NDI can receive, format and send data from the signal conditioning devices to the network controller. As the present invention is focused on the controller, the various embodiments below do notmention the communication between the network controller and NDI, but instead depict the remote device as communicating with the network controller. It must be understood that in some embodiments, the remote devices will include needed components to properly communicate with the network controller, while in other embodiments, a NDI will be needed. As such, the various communications of the remote devices discussed below may be performed by either the remote device or a NDI. A complete detailed disclosure of such a NDI is provided in U.S. Provisional Patent Application Number 60/254,136 entitled: NETWORK INTERFACE DEVICE FOR DIGITALLY INTERFACING REMOTE DEVICES TO A CONTROLLER VIA A NETWORK and filed on December 8, 2000, and U.S. Patent Application Number 09/735,146 entitled: NETWORK DEVICE INTERFACE FOR DIGITALLY TNTERFACING DATA CHANNELS TO A CONTROLLER VIA ANETWORK filed on December 12, 2000. The contents of this patent application are incorporated in its entirety herein by reference. As described above, the network controller 32, coupled with the network protocol and host computer 30, allows the network 25 to communicate with various remote devices 36, such as sensors, actuators and subsystems. More particularly, the network controller controls a network bus 34 that interconnects the remote devices to the network controller. The network controller uses the network bus to send commands to the remote devices and receive responses from the remote devices. Within the network, the network controller is typically controlled by the host computer. By default, the host computer is generally responsible for initializing the network bus at startup, sending the initial commands and resetting all hardware. Additionally, the host computer acts as the initial network controller at power-up. Further, in some embodiments, the host computer may also act as the operational network controller. Likewise, the network controller 32 may also contain the intelligence to be responsible for initializing the bus at startup, sending the initial commands and resetting all hardware. Additionally, the network controller may act as the master network controller, i.e., host computer 30, at power-up, thus having the capability to issue a stream of preprogrammed commands to the network and return data through the network controller to the host computer. The network controller may also alter the message arguments of the preprogrammed commands from data provided by the host computer. Such an embodiment can permit processor-free, time-deterministic operation of the network while still permitting control information to be processed and passed to the network. The network controller 32, on the other hand, performs the functions of the host computer 30 when it passes control to the network controller. Because the network controller is capable of performing, and many times performs, the functions of the host computer, the following description of the network, including the functions of the host computer, will be described with reference only to the network controller. Additionally, although several of the functions of the network controller are performed either through hardware, such as state devices and/or Applicati on Specific Integrated Circuits (ASIC), or through software, it should be noted that many hardware functions can be performed using software and vise versa without departing from the spirit and scope of the present invention. In addition to the network controller 32 operating as the master network controller, i.e., host computer 30 in one embodiment, in another embodiment the network controller can be configured to operate as a remote device 36 on the network 25. In this embodiment, the network controller can act as a NDI to another, subsystem host computer on the network 25. In this embodiment, the network bus 34 provides an intersystem connection between the host computer and the subsystem host computer. As such, the various communications between the network controller and the remote devices discussed below may be performed either between the network controller and the remote devices or NDIs, or the network controller and other network controllers, acting as NDIs. In addition to the capabilities of the NDI, operating as a remote device 36, the network controller 32 adds additional memory capabilities that may not be available in the NDI. The NDI contains a set of memory, referred to as a Transducer Electronic Data Sheet (TEDS), that stores configuration and calibration data. Each network device, including each network controller, will contain a TEDS. Some of the memory areas included within the TEDS are not changeable by the user. Other areas are mandatory user areas for information such as logical and group addresses and an ASCII description area, and yet other areas are not mandatory. Advantageously, for a network controller operating as a remote device, this additional space can be used to access large blocks of memory, typically random access memory (RAM) and/or EEPROM memory, within the remote device's host computer. This allows the master network controller to access not only the stack memory, like on an NDI, but also the RAM and/or EEPROM memory locations in the remote device's (i.e., network controller acting as a NDI) host computer. Because the network controller 32 of the present invention connects to the remote devices via a common network 25, the network controller does not require dedicated connections to each remote device to control the network. The network controller instead uses an addressing scheme to assign and control each of the remote devices 36. To operate the network, each remote device is assigned one or more addresses, including a logical address, global address and, if configured, one or more group addresses. A logical address is an address recognized by a single remote device that the network controller uses to direct a command, or request, to a particular remote device. A global address, on the other hand, is an address recognized by all of the , remote devices on the network which the network controller uses to exchange universal data and commands. For example, the global address scheme permits the network controller to universally initialize or reset all of the remote devises. A group address is an address that can be recognized by a particular group of remote devices on the network which the network controller uses to exchange group data and commands. For example, the group address scheme permits the network controller to set up time deterministic triggers for groups of remote devices at various sample rates. Referring now to FIG. 2, which depicts the network controller 32 electrically connected to a host computer 30 and a network bus 34. The network controller can contain an optional memory device 58, typically an EEPROM, RAM or Dual Ported RAM, that is electrically connected to the host computer. The memory device is designed to house a set of microcodes comprising control type commands for the network controller, such as timing schemes for collecting data from or providing data to the remote devices 36 connected to the network bus. In addition, the memory device is designed to house the network protocol commands for the remote devices, such as measuring data and transmitting data to the network controller. Optionally, the host computer can additionally select microcode commands 112 from the memory device for the network controller to perform. The network controller also includes a bus controller 44 that receives the microcodes, either from the memory device or the host computer, processes the microcodes and passes data when specified by the microcode. The network controller further includes a bus clock generator 56. The bus clock generator, running from either alocal oscillator 57 or an external clock 59 in various embodiments, generates multiple timing signals that the network controller can use for various functions, such as logic operations, baud generation, synchronous clock generation and asynchronous message receiving. The local oscillator can be selected to run at a multitude of different frequencies. For example, in one embodiment, the local oscillator operates at a frequency of 80 MHz. Because many of the functions of the network controller that use the clock do not require such a high frequency, the bus clock generator divides the local oscillator frequency by a specified divisor, typically sixteen. This divided clock signal is available as an output signal 61 that can be used to synchronize the network controller 32 to another network controller, not shown. Similarly, the external clock input 59 can be used to synchronize the network controller with another network controller, not shown. A controller transmitter 48, electrically connected to the bus controller 44, receives the data from the bus controller and formats the data into bit frames based on the communications protocol understood by the remote devices, such as a Manchester encoded Bi-Phase Sensor and System (BiSenSys) protocol. The BiSenSys protocol encodes messages by translating a voltage transition from a high state to low state as a binary "1" and a voltage transition from a low state to a high state as a binary "0." The controller transmitter then sends the bit frames, along with a clock signal, via a data transmitter 50 and a clock transmitter 52, respectfully, to the network bus 34 and, eventually, the remote devices. A data receiver 54, included within the network controller, receives message frames from the remote devices, through the network bus 34, and passes the data to the network receiver 46. The network receiver, in turn, processes the message frames, formats them from their encoded form and passes them to the host computer 30. Additionally, the network receiver uses the various characteristics of the received message frames to determine any transmission errors within the message frames, such as message frame errors 120, bi-phase encoding errors 114, parity errors 116 and error flag errors 118. The elements of the network controller 32, including the bus controller 44, bus clock generator 56, controller transmitter 48, data transmitter 50, clock transmitter 52, data receiver 54 and network receiver 46 may be of a variety of types. But while they must all be compatible with one another, they can comprise any of a variety of typical such elements, such as is known to those skilled in the art. Additionally, however, the elements that send and receive data from the network bus, are selected based on the type of network implemented. For example, a physical layer such as RS- 485, or TIA EIA-485-A, standard half-duplex multidrop network allows multiple RS- 485 compliant transmitters and receivers to reside on a single network line, with only one transmitter active at any given time. Additionally, the network controller can support a full duplex configuration network bus 34 where messages are simultaneously transmitted between the network controller and an active remote device 36. Also, while the elements described and illustrated are separate from one another, they can be implemented in a single or in multiple combined elements, such as in a field programmable gate array 60, without departing from the spirit and scope of the present invention. The physical layer can consist of many different transfer configurations, including differential twisted pair copper wire, coaxial copper wire, fiber-optic cable and radio frequency transmission. Physical layers, such as theRS-485 standard, allow the network to support high speed bit transfer rates. But in embodiments where low bit rates are required, such as in the kilobit range, a single-ended copper network bus, with a common, ground return path may be used. In such embodiments, the controller transmitter 48 and network receiver 46 can be used to transmit messages and clock signals to and receive messages from the remote devices, and elements outside the field programmable gate array 60, such as a separate data transmitter 50, clock transmitter 52 and data receiver 54, are not required. As mentioned above, the network controller 32 of the present invention operates in conjunction with a protocol that allows remote devices to communicate over a simple and high-speed yet robust digital multi-drop network 25. It must be understood that any applicable network protocol or physical layer, such as fiber-optic or wireless schemes, could be used in conjunction with the network controller of the present invention. However, described below is a particular protocol that provides several advantages when used in the network 25 illustrated in FIG. 1. One important advantage being that the simplicity of the protocol allows the network controller to communicate with remote devices 36 comprising state machines, as opposed to high- level processors. In operation, the network 25 runs in various formats and modes based on the command protocol and communication type implemented (i.e., synchronous or asynchronous). The command protocol format is determined by the command protocol compatible with the physical layer of the operational remote devices connected to the network, such as the Manchester encoded format or the format compatible with a Universal Asynchronous Receiver Transmitter (UART) physical layer, such as are known to those skilled in the art. It is not mandatory to support both the Manchester encoded format and UART physical layer on the network. Selection of the format is set within the network controller 32 and can be selected using software. Command and data messaging within the network protocol can be formatted to operate with both the Manchester encoding and UARTs. With the Manchester encoding, the network protocol comprises 18-bit message frames that include command frames and data frames. Command frames are used to pass addresses and commands from the network controller to one or more remote devices. Each command frame consists of a command sync pattern, a 7-bit command word, a 10-bit address word and a parity bit. Data frames, can be used as arguments to command frames or responses from one or more remote devices issued in response to commands from the network controller. Each data frame consists of a data sync pattern, a 16-bit data word, an error flag bit and a parity bit. The error bit is used by the remote devices 36 to inform the network controller 32 of the occurrence of an error within the remote device. Once the network controller receives the error flag from the remote device, the network controller can either issue commands such as Read Status Register, discussed below, to the remote device to try and determine the nature of the error. Advantageously, the use of the error flag bit allows the network controller to receive output data from the remote devices along with the error flag, instead of only receiving an error notification, such as an error word. With the Manchester encoding, the network can operate at any data rate from DC - to a high bit rate such as 10 MHz or higher in synchronous mode or at several predetermined bit rates in asynchronous mode. Distinguished from the Manchester encoding method, in UART mode, the network 25 is designed to typically operate at one bit rate and use non-return-to-zero (NRZ) bit coding. UART message frames contain three required 11 -bit frames, including address, command and checksum frames, and two optional 11 -bit frames, including number of data and data frames, utilized depending upon the command issued by the network controller. The first bit in every frame will be a start bit (set to "0"). The final bit of all frames is a stop bit (set to "1"). Additionally, the tenth bit is used by all frames is used to identify the first frame of a message (i.e., the address frame). The communication format implemented by the network 25 can include either synchronous or asynchronous communication, depending on the operational remote devices or control of the network controller. Using the Manchester encoding method, the communication format can be enabled by the network controller 32, and automatically detected by the remote devices 36 monitoring the network for synchronous clock tines. The network, using the Manchester encoded method, can typically be used synchronously at any bit rate between DC - to a high bit rate such as 10 MHz or higher, and the network controller and remote devices can operate asynchronously at several predetermined bit rates, such as 10 K, 20K, 1.25M, 2.5M, 5M, and 10M bits/sec. The lower bit rates permit single-ended physical layers reducing wiring costs and transceiver costs. High bit rates in the Mbit/sec range require differential copper signaling, fiber-optic, coaxial, or some other high-integrity signaling physical layer. Using the UART physical layer, the network typically operates at 1.0 or 1.25 Mbits/sec. With regard to the Manchester encoding method, in the synchronous mode, the clock generator 56 of the network controller provides a continuous synchronous clock signal. The synchronous clock signal is used by the remote devices of the present invention in the synchronous mode to clock in data from the network controller and to clock data out to the network controller. With the Manchester encoding method, operating asynchronously, a synchronous clock signal is not transmitted, and the network controller 32 operates at a predetermined bit rate. During operation, the network controller may alternate between a synchronous and asynchronous mode. Ifthe network controller changes to the asynchronous mode during operation, the bit rate is initially set at the lowest bit rate. The bit rate can then be changed using a Baud Select command, as described below. The remote devices 36 detect whether the network controller is operating in the synchronous or asynchronous mode by sensing whether the clock generator 56 is providing a synchronous clock signal, and adjusting their operation accordingly. If the network controller does alter the bit rate once the network enters asynchronous mode, the data transmitter 50 transmits data at the new bit rate to the remote devices. The remote devices, in turn, alter their output bit rate and send messages and data back to the data receiver 54 at the new bit rate. But before the data transmitter transmits operational commands to the remote devices, it may issue a null command to the remote devices to insure the remote devices resynchronize with the network controller at the new bit rate. As described above, each remote device 36 is provided with a logical address that uniquely identifies the remote device. Further, there is a global address that addresses all channels of all remote devices, and multiple group addresses that address a number of remote devices. The global address is used for the exchange of global data and commands. The group address is an address that can be recognized by multiple remote devices and is used for the exchange of data and commands to a group or subset of remote devices on the network. Associated with the group address is a group mask stored in the remote device. The group mask is a 16-bit word, representing 16 predetermined network addresses, where each bit set to "1" represents an address of the group that the remote device belongs. As an example, in one embodiment, the global address is assigned as OOOOhex. In this embodiment, ifthe network controller 32 transmits the address OOOOhex, all of the remote devices will follow the command. The network controller typically uses this command for service commands, triggering, resetting the system or testing the network 25. Further, in one embodiment, the group addresses are selected in the range of OOOlhex to OOOfhex, representing the range available in the remote device's group mask. In this embodiment, when the network controller transmits an address in this range to a remote device 36, the remote device will compare the group address with the group mask it has stored. If the bit in the group mask corresponding to the group address is set, the remote device will interpret and follow the command associated with the group address. For example, ifthe remote device has the group mask 100000001 lOObin stored, the remote device belongs to group addresses OOOfhex, 0003hex, and 0002hex. The group address scheme is designed to permit the network controller 32 to set up time-deterministic triggers for groups of remote devices 36 at various sample rates. Table 1 illustrates a group of sensors having different sample rates and their group assignments, and Table 2 illustrates the sequence for polling the sensors. Table 1 Table 2 With regard to the group addresses, ifthe network controller 32 sends out a group address, the remote device will decode the address portion of the command and compare the group address to the group mask stored in the remote device. Ifthe group mask indicates that the remote device is a member of the group address, the remote device will perform the command associated with the group address. As stated previously, the network controller of the present invention operates in conjunction with a selected protocol, hi one embodiment, this protocol is designed to insure low-level communication control interfaces, (i.e., network controllers 32 and remote devices 36). This protocol makes possible the development of controller and network interfaces that are highly miniaturized within the network 25. Ifthe network controller and remote devices are implemented using an ASIC, in conjunction with the protocol, the network controller and remote device can respond quickly and efficiently allowing for maximized bus efficiency. The protocol of the present invention also has a low overhead command structure. It does not use a fixed length message. The length of the message varies depending on the command. This, in turn, permits the elimination of unnecessary data being transmitted, if it is not needed to execute a function. In addition, the command set associated with the protocol is minimal and straightforward allowing the user to easily pass data through the network bus 34 with minimal manipulation. Generally, the commands included within the command set of the protocol fall into three broad categories, service commands, data commands and memory commands. Many of the commands of the network protocol are described below in Table 3. It should be noted, however, that the description of the commands below are intended to be illustrative, and not exhaustive, of the commands within the command set the network controller and remote devices can interpret. Some of the described commands may not be implemented in some embodiments, and other commands may be used in other embodiments, without departing from the spirit and scope of the present invention. A detailed disclosure of the commands directed at remote device processing is also provided in U.S. Provisional Patent Application Number 60/254,136 entitled: NETWORK INTERFACE DEVICE FOR DIGITALLY INTERFACING REMOTE DEVICES TO A CONTROLLER VIA A NETWORK and filed on December 8, 2000, and U.S. Patent Application Number 09/735,146 entitled: NETWORK DEVICE INTERFACE FOR DIGITALLY INTERFACING DATA CHANNELS TO A CONTROLLER VIA A NETWORK filed on December 12, 2000. Table 3 As described previously, the host computer 30, by default, issues many commands 110 directly to the network 25, including initializing the network bus 34 at startup, sending the initial commands and resetting all hardware. The host computer may also send commands and receive responses directly from the network. Likewise, as previously stated, the network controller 32 may also contain the intelligence to be responsible for initializing the bus at startup, sending the initial commands and resetting all hardware. Also, the network controller 32 may act as the master network controller, i.e., host computer, at power-up, thus having the capability to issue a stream of preprogrammed commands to the network and return data through the network controller to the host computer 30. Additionally the network controller 32 may alter the message arguments of the preprogrammed commands from data provided by the host computer 30. Such an embodiment can relieve the processor of consuming tasks and permit processor free time-deterministic operation of the network while still permitting control information to be processed and passed to the network. In one embodiment, control of the network can be passed temporarily from the host computer 30 or network controller 32 to a remote device 36 that has the capability of network control (and that may also be controlled by a host computer) using a Control Pass command. This permits other devices on the network bus 34 to issue commands and receive responses without the network controller 32 scheduling the commands. Such an application would be useful for remote devices capable of network control that need to acquire or pass significant information that is unique and not necessary for the network controller. The network controller has the capability of regaining control by issuing a Reset command which would perhaps conflict with traffic on the network bus, but would cause the remote device with temporary control to become silent, and allow the remote device to receive another Reset command indicating loss of control. In order for the network controller 32 to have full control over the remote devices 36, the network protocol includes several service commands, including several testing commands, such as Built-in-Tests, E-Calibration and Z-Calibration. To maintain remote devices and allow them to check their internal circuitry, the network controller can issue a Built-in-Tests command to the remote devices. While the network controller controls when these tests are performed, the remote device manufacturer defines the nature and scope of the tests performed by each remote device. The network controller uses the E-Calibration and Z-Calibration commands to generate a calibration measurement in the remote devices. Issuing an E- Calibration command, the network controller initiates the remote device to replace its input with a known reference voltage and take a measurement using the Trigger command, described below. Similarly, when the network controller issues a Z- Calibration command, the remote device shorts out its input and takes a measurement using the Trigger command. These commands allow the network controller to compare a known measurement against the actual value measured by the remote devices during the test. Additionally, these commands may also permit the initiation of an auto calibration procedure built in to the remote device setting the devices to a predetermined calibration when instructed. Also included within the service commands are No Op, Reset, Read Status Register, Wake, Sleep and Synchronize commands. The network controller issues the No Op command to the remote devices, typically along with another command, to instruct the remote devices to take no action or generate any response. When the network controller 32 wants to initialize the remote devices 36 to their power-up state, the network controller issues a Reset command 102. This command is used by the network controller to reset the network bus 34 and remote devices when necessary, and used by the host computer 30 and/or network controller to regain control of the network from another host computer and/or network controller that has temporary control of the network. Additionally, this command can be used by a remote device manufacturer to perform other resetting functions within a remote device. To access the status of a remote device, or multiple remote devices, the network controller issues a Read Status Register command to the remote devices. In response to this command, the selected remote devices will transfer the contents of its status register to the network controller indicating the status of the remote device, such as device not ready error, device does not support command error, message transmission error, invalid argument error or that a built-in-test has been performed since the last status read. To control the power draw of the remote devices 36 on a network 25 equipped with current limited power leads, the network controller will issue Wake and Sleep commands to the remote devices. The network controller 32 uses the Wake command to wake up a remote device in power down mode. After receiving this command, the remote device will return to normal operating mode. To put a device in power down mode, the network controller issues a Sleep command. This command will cause a remote device that will not be interrogated by the network bus 34 for a significant amount of time to reduce power draw from the network. Some remote devices use oversampling techniques such as Sigma-Delta converters to acquire data. To synchronize the acquisition of oversampling devices using the clock generator 56 of the network controller 32, the network controller issues a Synchronize command. When issued, the selected remote devices synchronize their data acquisition on the next synchronous clock edge following the changing center edge of the parity bit in the trigger command message. Ifthe device has an internal clock signal for running the Sigma-Delta converter that is synchronous with the clock generator signal, butis some fraction of the bus clock signal, the remote device will align itself with the clock generator signal. This will allow multiple remote devices to run substantially synchronously. Ifthe sample and hold do not occur at this time, the remote device manufacturer will define the delay in clock cycles of the remote device. As mentioned above, the network controller 32 addresses each of the remote devices by a logical, group and global addressing scheme. To begin implementation of the network 25, the network controller 32 inventories the remote devices 36 on the network and assigns the logical and, if configured, group addresses to those devices. Although the network controller can perform the inventorying and addressing by any conventional method, it typically performs such functions via a device inventory session. Using the Manchester encoded method, the network controller performs the device inventory session using a universal unique identifier (UUID) stored on each remote device, as illustrated in FIG. 3. Every remote device, at the time of manufacture, is assigned a UUID code that is derived by each device' s manufacturer based on a defined set of criteria. The UUID consists of an 80-bit code that is used as a unique identifier that no other devices can posses. Due to the excessive length of the UUID, however, it is too long for the network to implement in the addressing scheme for the remote devices. UART compliant devices can contain a UUID , however, they cannot perform a device inventory. Therefore, in UART mode, the network controller individually assigns logical and group addresses to UART compliant remote devices as those devices are connected to the network. During the device inventory session using the Manchester encoded format, the network controller 32 determines the UUIDs of the each remote device 36 by performing a UUID word search. The UlUD word search, in turn, includes what is known as a bit competition to ensure that the network controller receives and assigns addresses to only one particular UUID at a time. A device inventory session, begins with the network controller issuing a Device Inventory Enable command with a global address or a group of addresses (from a previous device inventory). At this point all devices within the address group are in device inventory mode. Once in the device inventory mode, the address field in the command frame becomes a function code field (hereinafter function codes will be represented in parenthesis after its respective command) as illustrated in FIG. 2 and blocks 200 and 300 of FIGS. 3 and 4, respectively. The network controller then issues a Device Inventory {New UUID Word Search) command to the remote devices indicating that the session is beginning a new UUID word search, as illustrated in block 201 of FIG. 3 and block 302 of FIG. 4. Then, the network controller begins the bit competition by issuing Device Inventory (UUID Bit Competition, No Dropouts) command, instituting what is known as a "No Dropout" function wherein the devices identify and evaluate the least significant bit of their respective UUIDs, as shown in block 204 of FIG. 3 and blocks 304 and 306 of FIG. 4. If the identified bit is a "0," the remote device transmits a pulse on the network 106 to the network controller, as. shown in FIG. 2 and blocks 308 and 310 of FIG. 4. If a pulse is detected on the network and the current bit is not the eightieth bit (80) (i.e., the most significant UUID bit), the network controller stores the signal as a "0" in a UUID memory location, as shown in blocks 206 and 208 of FIG. 3 and block 312 of FIG. 4. Ifthe remote device's current bit is a "1," the remote device doesn't send a pulse to the network controller. If no remote devices send a pulse to the network controller and the identified bit is not the eightieth bit, the network controller stores a"l" in the UUID memory location, as illustrated in blocks 212 and 214. While the UUID memory location can comprise any conventional device thatis capable of atleast temporarily storing values, it typically comprises a shift register. After the remote devices 36 evaluate the identified bit, each remote device shifts the identified bit into a secondary location and identifies its next least significant UUID bit, as illustrated in block 314 of FIG. 4. If the network controller 32 has stored a " 1" in the UUID memory location, the network controller reissues the Device Inventory (UUID Bit Competition, No Dropout) command to the remote devices, as illustrated in block 216 of FIG. 3. The remote devices then repeat the process identified above depending upon whether the newly identified bit is a "0" or "1." If, on the other hand, the network controller has stored a "0" in the UUID memory location, the network controller issues what a Device Inventory (UUID Bit Competition, I 's Dropout) command, initiating what is known as a "1 ' s Dropout" function to the remote devices, as shown in block 210 of FIG. 3 and block 326 of FIG. 4. If aremote device's bit stored in the secondary location is a "1," the remote device exits the bit competition and waits for a New UUID Word Search command to reenter the competition, as shown in block 326. Ifthe remote device's bit stored in the secondary location is a "0," the remote device evaluates its newly identified bit, following the procedure described above. The procedure then continues with each of the remote devices' UUID bits, completing 81 iterations of the procedure to allow for the winning remote device to determine it won the bit competition, as shown in blocks 218 and 220. As each remote device' s UUID is found by winning the bit competition, as shown in block 316 of FIG. 4, the remote device 36 is assigned its logical and group addresses which are stored along with any desired TEDS information needed in the remote device, as illustrated in blocks 221 and 222 of FIG. 3 and blocks 318-324 of FIG. 4. This information is typically stored in a memory device, such as an EEPROM, on the remote device. The network controller 32 then issues the Device Inventory (Protect/Exit Device Inventory Mode) command which causes the winning remote device to exit the device inventory session, as shown in block 223 of FIG. 3. The network controller then starts the procedure over, as illustrated in block 201- until all devices have been identified. The network controller recognizes when all of the devices have been recognized when all 80 bits in the bus controller' s UUID register are "l's," as shown in block 224. When the UUID of every remote device on the network 25 has been searched and determined, the network controller 32 will issue a Device Inventory (All Exit Device Inventory) command and, thus, complete the inventory, as illustrated in block 225. Typically, the device inventory session will only have to be completed once the network is assembled or changed. But a device inventory session can be run at any time to verify the network configuration or to insure the network is configured. As described previously, the network 25 is capable of operating at different baud rates. When operating in asynchronous mode, the network will default to the lowest baud rate configured for the network. The network controller 32 can change the baud rate of data transmission by issuing a Baud Select command 108, as shown in FIG. 2. To insure the remote devices 36 resynchronize at the new communication speed with the network controller, the network controller must issue a No Op command following the Baud Select command. Once the network controller 32 has inventoried and assigned addresses to the remote devices 36, the network controller can issue commands to the remote devices to send data to and receive data from those devices. In order for the network controller 32 to have full control over the remote devices 36, the network protocol includes several data acquisition and control commands, such as Trigger, Trigger and Read, Read In-Data Register Word, Read In-Data Stack Word, Read In-Data stack Block, Query In-Data/Out-Data Stack Depth, Write Out-Data Stack Word, Write Out-Data Stack Word/Echo to In-Data Register and Write Out-Data Stack Block. These commands are used to address a sequential type of memory in remote devices that resembles a stack of memory that is accessed by pushing data on or popping data off of the top of a stack of memory locations. To initiate an incoming data measurement in a sensor or move a value to an output in an actuator in all devices that belong to a logical and/or group address, the network controller will issue a Trigger command to those devices. Following a data measurement, ifthe network controller wants to receive the measurements taken by the remote devices, the network controller will issue a Read In-Data Stack Word command to each of those devices. If multiple trigger commands are issued to the remote devices, the Read In-Data stack Block command issued to each device will return the multiple measurements taken. Additionally, along with receiving data from remote devices, the network controller can additionally write data to the remote devices by issuing a Write Out-Data Stack Word, Write Out-Data Stack Word/Echo to In-Data Register, or Write Out-Data Stack Block command. It should also be noted that even though a Read command typically follows a Trigger command, the network controller can issue the Read command at any time as long as the remote device has a data value stored within it. Trigger commands typically follow a write command to the remote device, which then cause the output of the remote device to be updated with the value or group of values of the previous Write Out-Data commands. To initiate a measurement cycle in a remote device 36 and immediately transmit the results of the previous measurement cycle onto the network bus 34, the network controller 32 will issue a Trigger and Read command. Because the network 25 generally only supports data transmission from a single remote device at any given time, Trigger and Read commands are generally limited to unique logical addresses only, and will not use group addressing. To determine how many valid data words are stored in a selected remote device, the network controller will issue a Query In- Data/Out-Data Stack Depth command to a specific logical address. The remote device, in turn, responds by transmitting to the network bus the number of valid words stored. In addition to reading or writing to a data stack on the remote device 36, the network controller 32 can additionally read from or write to the memory of the remote devices by issuing a number of random access memory commands, including Read Memory and Write Memory commands. This memory can represent many different memory locations, such as the mandatory TEDS information contained within the remote device or additional memory space within the remote devices host computer. The network controller can read from the memory of a remote device by issuing a Read Memory command. To read a length of memory, either a word or block, the network controller will issue a Read Memory Word with Passed Pointer command and additionally specify the memory location. Additionally, the network controller can set the remote devices memory pointer by issuing a Set Memory Pointer command and then issue a Read Memory Word with Current Pointer command . Likewise, the network controller can write to either a word or block of memory on a remote device by issuing a Write Memory Block with Passed Pointer command and additionally specify the memory location. Additionally, the network controller can set the remote devices memory pointer by issuing a Set Memory Pointer command and then issue a Write Memory Block with Current Pointer command. Referring now to FIG. 5, as previously stated, the avionics industry provides a typical application of the network controller. For example, the network controller 22 can be used on an aircraft 10 to control and monitor actuators and sensors. The aircraft can use the network to monitor various critical structural locations for strains 12, such as wing root, wing surface, tail root, tail cord and landing gear strains, and accelerations 14, such as wing tip and tail tip accelerations. Additionally, the network can be used to monitor the pressure 16 at various critical structural locations, such as critical belly pressures for sonic fatigue, as well as key corrosion locations 18 for radar, landing gear and leading edges, and engine casing temperatures 20. The network controller of the present invention therefore allows network components to communicate over an inexpensive, simple and high-speed, yet robust, network line with a simple message protocol, small component size and low wire count. The network controller can also advantageously operate without the use of a microcontroller or processor for the network components using either a Manchester encoding or UART command protocols, thereby reducing the overhead associated with an associated host processor and allowing the entire network to run via the controller's single clock signal. Also, the network controller supports both acquisition and control, acquires data simultaneously from the components and operates with synchronized data samples from the components. The network controller can be used for efficient, time-deterministic, high-speed acquisition and control, and intersystem data transfer. Further, the network controller allows for high component counts, longer network lines and insures time determinism in a precise manner. As illustrated in FIG. 5, the network controller of the present invention may be implemented in a monitoring system for monitoring various portions of an object, such as an aircraft or automobile. In some embodiments, such as in an aircraft, the various sensors and actuators of the monitoring system may be spread throughout the aircraft at different locations of interest. For example, in some applications, the monitoring system may include a first set of sensors and actuators located about or near the tail of the aircraft, a second set at or about the wings, and a third at or about the cockpit, with an elongated network bus line between the sets of sensors and actuators. As discussed previously, however, the use of metallic wiring, such as wiring made of copper, has some drawbacks due to DC resistance thatmay degrade commands and data transmitted on the network bus. This problem with metallic wiring may become troublesome in instances where there are elongated spans between, for example, the first set of sensors and actuators located at the tail of the aircraft and the second set of sensors and actuators located at the wing of the aircraft. Specifically, an elongated metallic wiring acting as the bus link between these two sets of sensors and actuators may degrade command and data communication on the bus. In light of this, with reference to FIG. 6, in one embodiment, the present invention provides a translation device 330 that transitions from metallic wiring used by the network bus to connect the sensors and actuator of the first set located at the wing to metallic wiring used to interconnect the sensors and actuators of the second set located at the wing or cockpit using a fiber optic cable. This is advantageous because fiber optic cable typically does not degrade signals significantly as they propagate along its length, thereby allowing the first and second sets of sensors and actuators to be spaced relatively far apart without concerns of signal degradation during propagation across the distance between the first and second sets. For example, FIG. 6 illustrates a first metallic line 332 that is connected to a first set of sensors and actuators located at a position of an object and a second metallic line 334 connected to a second set of sensors and actuators located at a different position on the object. Connecting the first and second metallic wiring is a set of fiber-optic cables 336 or similar type cables that minimally degrade signals due to length. Between the fiber-optic cables and each copper wire is a translator device 330 for transitioning the signals propagating on the metallic line into optic signals and vice versa. Importantly, in this illustrative embodiment, the metallic lines are a half- duplex bus, while the fiber-optic cable is full-duplex. In light of this, not only do the translation devices of the present invention transition the commands and data present on the network bus to optical data for transmission across the fiber-optic cable, but they may also translate the commands and data from a half-duplex system to a full- duplex system and vice versa. In this embodiment, the translation devices of the present invention may include an S-485 transducer for receiving and transmitting data. Connected to the transducer is logic that translates the commands and data located on the network bus between half and full-duplex for transmission across the fiber-optic cable and copper wires. Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims: WHAT IS CLAIMED IS: 1. A network controller for digitally directing communications with a plurality of remote devices via a common bus, the network controller comprising: a transmitter for digitally transmitting messages via the common bus; a receiver for receiving digital messages from the common bus; and a clock for providing clock signals to both said transmitter and said receiver, wherein both said transmitter and receiver are capable of selectively operating in either mode selected from the group consisting of a synchronous mode and an asynchronous mode, wherein said transmitter transmits both messages and the clock signals via the common bus in the synchronous mode, and wherein said transmitter transmits messages at a predetermined bit rate without any accompanying clock signals via the common bus in the asynchronous mode. 2. A network controller according to Claim 1 further comprising a clock transmitter for digitally transmitting the clock signals via the common bus, wherein said clock transmitter operates at a constant level during the asynchronous mode. 3. A network controller according to Claim 1 wherein said clock receives a baud select command that defines the predetermined bit rate at which said transmitter will transmit messages in the asynchronous mode. 4. A network controller according to Claim 1 wherein said network controller is capable of commanding a remote device to at least temporarily direct the communication with the other remote devices via the common bus. 5. A network controller according to Claim 1 wherein said receiver asynchronously receives messages from the common bus. 6. A network controller according to Claim 1 wherein the common bus is selected from a group consisting of differential twisted copper wire, coaxial copper wire, fiber-optic cable and single-ended copper wire. 7. A network controller according to Claim 1 wherein the network controller is capable of selectively operating in either communication mode selected from the group consisting of a half-duplex communication mode and a full-duplex communication mode. 8. A network controller according to Claim 1 wherein said network controller is capable of acting as a remote device while another, master network controller directs communications with the plurality of remote devices, including the network controller, via the common bus. 9. A network controller according to Claim 8, wherein said network controller is capable of interacting with a host computer having stack memory and random access memory (RAM), wherein when said network controller is acting as a remote device, the master network controller is capable of selectively accessing either type of memory selected from the group consisting of the stack of sequential memory and the RAM. 10. A network controller for digitally directing communications with a plurality of remote devices via a common bus, the network controller comprising: a transmitter for transmitting digital messages to the plurality of remote devices via the common bus at a predetermined bit rate, said transmitter being capable of altering the predetermined bit rate at whichmessages are transmitted while communicating with the plurality of remote devices; and a receiver for receiving digital messages from the plurality of remote devices via the common bus at the same predetermined bit rate at which messages were previously transmitted to the plurality of remote devices such that said receiver is capable of receiving messages as said transmitter alters the predetermined bit rate without relying upon any clock signals. 11. A network controller according to Claim 10 wherein said transmitter transmits an example message to the at least one remote device at an altered bit rate following alteration of the predetermined bit rate. 12. A network controller according to Claim 10 wherein said transmitter receives a baud select command that defines the predetermined bit rate at which the messages will be transmitted. 13. A method for digitally communicating between a network controller and a plurality of remote devices via a common bus, the method comprising: configuring the controller based upon a command protocol according to which the plurality of remote devices are capable of communicating, wherein the plurality of remote devices are capable of communicating according to a command protocol selected from the group consisting of Manchestpr encoding and a Universal Asynchronous Receiver Transmitter (UART) protocol; and transmitting messages between the bus controller and the plurality of remote devices according to the same command protocol with which the plurality of remote devices are capable of communicating. 14. A method according to Claim 13 wherein transmitting messages comprises transmitting messages according to the Manchester encoding command protocol if the plurality of remote devices are capable of communicating according to the Manchester encoding command protocol, and wherein transmitting messages according to the Manchester encoding command protocol comprises transmitting messages according to a mode selected from the group consisting of a synchronous mode and an asynchronous mode. 15. A method according to Claim 14 wherein transmitting messages in the synchronous mode comprises transmitting messages while concurrently transmitting a clock signal from the network controller to the plurality of remote devices via a common clock transmitter, and wherein transmitting messages in the asynchronous mode comprises transmitting messages at a predetermined bit rate without transmitting a clock signal. 16. A method according to Claim 14 wherein the messages comprise at least one message pulse, wherein transmitting messages according to the Manchester encoding command protocol comprises transmitting messages in the asynchronous mode, and further comprising synchronizing the messages using an edge of the message pulse. 17. A method according to Claim 13 wherein transmitting messages comprises transmitting messages according to the Manchester encoding command protocol if the plurality of remote devices are capable of communicating according to the Manchester encoding command protocol, and wherein transmitting messages according to the Manchester encoding protocol comprises transmitting messages comprised of a plurality of bits, each having a value defined by a transition between first and second states. 18. A method according to Claim 13 wherein transmitting messages comprises transmitting messages according to the Manchester encoding command protocol if the plurality of remote devices are capable of communicating according to the Manchester encoding command protocol, and wherein transmitting messages according to the Manchester encoding command protocol comprises transmitting messages comprised of a sync portion, a message body and a parity flag. 19. A method according to Claim 18 wherein transmitting messages according to the Manchester encoding command protocol comprises transmitting messages comprised of a sync portion, a message body including an error flag bit, and a parity flag. 20. A method according to Claim 13 wherein transmitting messages comprises transmitting messages according to the UART command protocol if the plurality of remote devices are capable of communicating according to the UART command protocol, and wherein transmitting messages according to the UART protocol comprises transmitting messages at a predetermined bit rate and according to a non-return-to-zero (NRZ) bit format. 21. A method according to Claim 13 wherein transmitting messages comprises transmitting messages according to the UART command protocol if the plurality of remote devices are capable of communicating according to the UART command protocol, and wherein transmitting messages according to the UART command protocol comprises transmitting an idle pattern to reset the plurality of remote devices prior to transmitting each message. 22. A method according to Claim 13 further comprising receiving a command protocol select command at the controller such that the subsequent configuration of the controller is based upon the command protocol select command. 23. A method according to Claim 13 wherein transmitting comprises selectively transmitting messages in either communication mode selected from the group consisting of a half-duplex communication mode and a full-duplex communication mode. 24. A network controller for digitally directing communications with a plurality of remote devices via a common bus, the network controller comprising: a transmitter for transmitting digital messages via the common bus; a receiver for receiving digital messages from the common bus; and a clock for providing clock signals to both said transmitter and said receiver, wherein both said transmitter and receiver are capable of selectively operating in accordance with any command protocol selected from the group consisting of Manchester encoding and Universal Asynchronous Receiver Transmitter (UART) protocol, wherein said transmitter and receiver are responsive to a command protocol select command that identifies the command protocol according to which the plurality of remote devices are capable of communicating such that said transmitter and receiver thereafter transmit and receive messages, respectively, in accordance with the command protocol identified by the protocol select command. 25. A network controller according to Claim 24 wherein said transmitter, while operating in accordance with the Manchester encoding command protocol, transmits messages according to the Manchester encoding command protocol, and wherein said transmitter transmits Manchester encoded messages according to a mode selected from the group consisting of a synchronous mode and an asynchronous mode. 26. A network controller according to Claim 25 wherein said transmitter transmits messages in the synchronous mode while concurrently transmitting a clock signal to the plurality of remote devices via a common clock bus, and wherein said transmitter transmits messages in the asynchronous mode at a predetermined bit rate without transmitting a clock signal. 27. A network controller according to Claim 24 wherein said transmitter transmits Manchester encoded messages comprised of a plurality of bits, each bit having a value defined by a transition between first and second states. 28. A network controller according to Claim 24 wherein said transmitter transmits Manchester encoded messages comprised of a sync portion, a message body and a parity flag. 29. A network controller according to Claim 24 wherein said transmitter transmits messages according to the UART protocol at a predetermined bit rate and utilizing a non-return-to-zero (NRZ) bit format. 30. A network controller according to Claim 24 wherein said transmitter, while operating in accordance with the UART command protocol, transmits an idle pattern to reset the plurality of remote devices prior to transmitting each message. 31. A network controller according to Claim 24 wherein said transmitter transmits messages via the common bus selected from a group consisting of differential twisted copper wire, coaxial copper wire and fiber-optic cable. 32. A network controller according to Claim 24 wherein the network controller is capable of selectively operating in either communication mode selected from the group consisting of a half-duplex communication mode and a full-duplex communication mode. 33. A network controller for digitally directing communications with a plurality of remote devices via a common bus, the bus controller comprising: a transmitter for transmitting digital messages via the common bus, said transmitter adapted to transmit messages comprising a command and an address of at least one remote device, said transmitter being further adapted to simultaneously transmit messages to a plurality of remote devices in accordance with a group address comprised of a plurality of bits with each bit associated with a respective group, thereby enabling said transmitter to direct a message to a group of remote devices by setting the respective bit of the group address; and a receiver for receiving digital messages from the common bus. 34. A network controller according to Claim 33 wherein said transmitter is also adapted to transmit messages to individual remote devices in accordance with a unique logical addresses assigned to the plurality of remote devices. 35. A network controller according to Claim 34 wherein said transmitter is also adapted to transmit messages to all of the plurality of remote addresses in accordance with a global address. 36. A network controller for digitally dire cting communications with a plurality of remote devices via a common bus, the network controller comprising: a transmitter for digitally transmitting messages via the common bus; and a receiver for receiving digital messages from the common bus, wherein the transmitter is capable of transmitting an indefinitely repeating sequence of predetermined messages via the common bus, the receiver is capable of receiving an indefinitely repeating sequence of messages from the common bus, and wherein the network controller is capable of altering the predetermined messages as the transmitter transmits messages and the receiver receives messages. 37. A network controller according to Claim 36 further comprising a clock for providing clock signals to both said transmitter and said receiver, wherein both said transmitter and receiver are capable of selectively operating in either mode selected from the group consisting of a synchronous mode and an asynchronous mode, wherein said transmitter transmits both the messages and the clock signals via the common bus in the synchronous mode, and wherein said transmitter transmits the messages at a predetermined bit rate without any accompanying clock signals via the common bus in the asynchronous mode. 38. A monitoring system for monitoring various locations of interest on an object comprising: a first set of remote devices located at a first position of interest on the object; a second set of remote devices located at a second position of interest on the object remote from the first position; a network controller for sending digital commands and data to and receiving data from the remote devices; and a common bus connecting each of the remote devices of each of said first and second sets of remote devices, wherein said common bus comprises: first electrical wiring for interconnecting each of the remote devices of said first set of remote devices together, and second electrical wiring for interconnecting each of the remote devices of said second set of remote devices together; and optical fibers for interconnecting the first set of remote devices at the first position to the second set of remote devices at the second position, wherein the use of said optical fibers to span from the first to the second position facilitates transmission of the commands and data between said network controller and the remote devices. 39. A monitoring system according to Claim 38 further comprising at least one translation device connected between one of said first and second electrical wiring and optical fibers, wherein said translation device translates electrical signals from said electrical wiring into optical signals for transmission across said optical fibers and translates optical signals from said optical fibers into electrical signals for transmission across said electrical wiring. 40. A monitoring system according to Claim 39, wherein said first and second electrical wiring of said common bus is half- duplexed and said optical fibers of said common bus are full- duplexed, and wherein said translation device translates digital commands and data transmitted on said common digital bus from half-duplex to full- duplex for transmission on said optical fibers and from full-duplex to half-duplex for transmission on said first and second electrical ' wiring. 41. A monitoring system according to Claim 40, wherein said translation device comprises: a transceiver in electrical communication with said electrical wiring and said optical fibers of said common bus for receiving and transmitting digital commands and data; and logic in electrical communication with said transceiver for translating electrical signals from said electrical wiring into optical signals for transmission across said optical fibers and translating optical signals from said optical fibers into electrical signals for transmission across said electrical wiring. 42. A monitoring system according to Claim 41, wherein said logic translates digital commands and data from said electrical wiring into full-duplex format for transmission across said optical fibers and translates commands and data from said optical fibers into half-duplex format for transmission across said electrical wiring.

Inventors: ELLERBROCK PHILIP J, KONZ DANIEL W, WINKELMANN JOSEPH P, ELLERBROCK, PHILIP, J., KONZ, DANIEL, W., WINKELMANN, JOSEPH, P.
Applicants: BOEING CO, THE BOEING COMPANY
Application year: 2001
Main classification: G06F13
IPC codes: H04L12, H04L25, H04L29, H04Q9