Abstract:
A sensor comprises a transmitter to transmit signals over a communication path, the sensor further capable to receive signals from the communication path, wherein the sensor is configured to communicate sensor data having a nibble data signal format at the transmitter in response to a trigger signal received at the sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This continuation application is a continuation of U.S. patent application Ser. No. 14/010,353 filed on Aug. 26, 2013 which is a continuation of U.S. patent application Ser. No. 13/444,023 filed on Apr. 11, 2012 now U.S. Pat. No. 8,519,819 which is a continuation of U.S. patent application Ser. No. 11/838,475 now U.S. Pat. No. 8,183,982 and claims the benefit of the priority date of the above application, the contents of which are herein incorporated in its full entirety by reference. 
     
    
     BACKGROUND 
       [0002]    Typically, an electrical system includes a number of different components that communicate with one another to perform system functions. The different components may be situated on the same integrated circuit chip or on different integrated circuit chips. Usually, an electrical system, such as the electrical system in an automobile, includes one or more controllers, memory chips, sensor circuits, and actor circuits. The controller digitally communicates with the memory chips, sensors, and actors to control operations in the automobile. 
         [0003]    In digital communications a common time base is used to transmit and receive data. The common time base needs to be provided to each of the components and can be provided to each of the components via an explicit clock signal or by combining the time base with the transmitted data. A transmitter transmits data via the common time base and a receiver receives and decodes the data via the common time base. The received data cannot be properly decoded without the common time base. 
         [0004]    Another aspect of digital communications includes the start time of a data transmission. If the transmission start time is not coded on the common time base signal or in the data, another signal line is used to indicate the start of a data transmission. Many embedded systems include a common system clock and selection signals that select system components and indicate the start of data transmissions. 
         [0005]    Often, in decentralized systems, a multi-wire communication system, such as a serial peripheral interface (SPI), is used. Typically, a master provides a clock signal and a slave select signal to each component via separate signal lines. The master toggles the clock signal coincident with transmitted data and the slave select signals select components and indicate the beginning and/or end of a data transmission. In operation of an SPI system, the master configures the clock signal to a frequency that is less than or equal to the maximum frequency of a slave and pulls the slave&#39;s select line low. The master selects one slave at a time. If a waiting period is required, the master waits for the waiting period before issuing clock cycles. During each clock cycle a full duplex data transmission occurs, where the master sends a bit on one line and the slave reads the bit from the one line and the slave sends a bit on another line and the master reads the bit from the other line. Transmissions include any number of clock cycles and when there are no more data to be transmitted, the master deselects the slave and stops toggling the clock signal. 
         [0006]    Separate clock and select signal lines to each of the components can be used to provide bus ability. In addition, in these systems the masters can send data to the slaves. However, separate signal lines increase costs and manufacturers want to reduce costs. 
         [0007]    To avoid using a separate clock line, the time base can be encoded into the data. For example, Manchester encoding is a bit-synchronous transmission method where data is transmitted bit by bit using a given bit rate. In Manchester encoding, each bit is represented by either a rising edge or a falling edge of an electrical signal, where the rising edge represents one of a logical one or a logical zero and the falling edge represents the other one of a logical one or a logical zero. Between bits the electrical signal may need to transition to transfer the next bit and it is necessary to distinguish between edges that represent bits and edges that are signal changes between bits. This is achieved by starting the transmission with a known bit sequence, referred to as a preamble. However, the preamble mechanism is for only a one-way transmission and the receiver is not able to control the start time of the transmission. Also, the transmission requires twice the frequency of the bit rate and high frequencies introduce electromagnetic interference (EMI) problems. In addition, dedicated circuits are needed, since it is difficult to encode and decode the data using typical peripheral elements found on embedded controllers. 
         [0008]    For these and other reasons there is a need for the present invention. 
       SUMMARY 
       [0009]    According to one aspect, a sensor comprises a transmitter to transmit signals over a communication path, the sensor further capable to receive signals from the communication path, wherein the sensor is configured to communicate sensor data having a nibble data signal format at the transmitter in response to a trigger signal received at the sensor. 
         [0010]    According to a further aspect, a sensor comprises a transmitter to transmit signals over a communication path, the sensor further comprising circuitry to receive signals from the communication path, wherein the sensor is configured to communicate sensor data over a communication path by transmitting a pulse width modulated data signal in response to a trigger signal which is received at the sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The accompanying drawings are included to provide a further understanding of embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain principles of embodiments. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. 
           [0012]      FIG. 1  is a diagram illustrating one embodiment of an electrical system according to the present invention. 
           [0013]      FIG. 2  is a block diagram illustrating a request signal and a reply signal in one embodiment of an electrical system. 
           [0014]      FIG. 3  is a diagram illustrating a reply signal that is transmitted via one embodiment of a transmitter. 
           [0015]      FIG. 4  is a diagram illustrating one embodiment of an electrical system that includes a controller, a first sensor, and a second sensor. 
           [0016]      FIG. 5  is a timing diagram illustrating the operation of one embodiment of the electrical system of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
         [0018]    It is to be understood that the features of the various exemplary embodiments described herein may be combined with each other, unless specifically noted otherwise. 
         [0019]      FIG. 1  is a diagram illustrating one embodiment of an electrical system  20  according to the present invention. In one embodiment, system  20  is part of an automobile&#39;s electrical system. 
         [0020]    System  20  includes a receiver  22  and a transmitter  24 . Receiver  22  is communicatively coupled to transmitter  24  via one or more communication paths at  26 . In one embodiment, receiver  22  is part of one integrated circuit chip and transmitter  24  is part of another integrated circuit chip. In one embodiment, receiver  22  and transmitter  24  are part of the same integrated circuit chip. In one embodiment, receiver  22  is a controller. In one embodiment, transmitter  24  is a sensor, such as an automobile sensor. In one embodiment, transmitter  24  is an actor, such as a relay circuit. In one embodiment, transmitter  24  is a controller. In other embodiments, receiver  22  and transmitter  24  are any suitable components. 
         [0021]    Receiver  22  transmits a request signal to transmitter  24  via one of the communication paths at  26  and transmitter  24  transmits a reply signal to receiver  22  via one of the communication paths at  26 . The reply signal includes a synchronization signal that indicates the time base of transmitter  24  and data. The request signal and the reply signal overlap in time, where at least a portion of the request signal occurs at the same time as at least a portion of the reply signal. In one embodiment, the request signal and the synchronization signal overlap in time, where at least a portion of the request signal occurs at the same time as at least a portion of the synchronization signal. 
         [0022]    Transmitter  24  transmits data correlated to the time base of transmitter  24 , where the length of the synchronization signal indicates the time base of transmitter  24  and the length of each data signal represents data bits. In one embodiment, each data signal represents a nibble of data, i.e. four data bits. 
         [0023]    Receiver  22  receives the synchronization signal and measures the length of the synchronization signal to obtain the time base of transmitter  24 . Based on the received time base, receiver  22  recovers data bit information from the data signals via measuring the length of the data signals and comparing the measured length to the received time base of transmitter  24 . In one embodiment, the request signal includes a trigger signal and transmitter  24  starts the reply signal in response to the trigger signal. In one embodiment, the request signal includes a trigger signal and transmitter  24  starts the synchronization signal in response to the trigger signal. In one embodiment, the request signal includes a trigger signal and the length of the synchronization signal is measured from the trigger signal to the end of the synchronization signal provided via transmitter  24 . 
         [0024]    In one embodiment, receiver  22  transmits one or more commands and/or data to transmitter  24  in the request signal. In one embodiment, the request signal includes one or more transmitter identification values to select one or more of multiple transmitters, which provides bus ability in system  20 . In one embodiment, the request signal includes data request parameters, such as sensor measurement range information that directs the transmitter to switch to a different sensor measurement range or transmit data in the specified sensor measurement range. In one embodiment, the request signal includes configurable parameters, such as relay turn-on/off time that directs a relay to remain on/off for a specified time. In one embodiment, the request signal includes commands, such as a self-test signal that directs the transmitter to perform a self-test or a memory test. In one embodiment, the request signal includes a wake-up signal that powers up the transmitter from a sleep mode or power down mode. In one embodiment, the request signal includes a power down signal to power down the transmitter or put the transmitter in a power saving sleep mode. In one embodiment, the request signal includes a send data and remain powered-up signal. In one embodiment, the request signal includes a send data and power down signal. 
         [0025]    In one embodiment, receiver  22  transmits a request and transmitter  24  transmits a pulse width modulated reply signal that includes a synchronization pulse followed by one or more data pulses. The synchronization pulse is the synchronization signal, where the length of the synchronization pulse represents the time base, i.e. clock speed, of transmitter  24 . Each of the data pulses represents one or more data bits of information, such as transmitter status, transmitter data, and checksum information. The request signal overlaps in time the pulse width modulated reply signal and the synchronization signal. Receiver  22  receives the pulse width modulated reply signal and measures the lengths of the synchronization pulse and the data pulses to recover data bit information. 
         [0026]    Receiver  22  transmits the request via one of the communication paths  26  and transmitter  24  transmits the reply signal via one of the communication paths  26 . In one embodiment, receiver  22  and transmitter  24  are communicatively coupled via one or more conductive lines, where each of the conductive lines is a communications path. In one embodiment, receiver  22  and transmitter  24  are communicatively coupled via one or more radio frequency (RF) frequencies, where each of the RF frequencies is a communications path. In one embodiment, receiver  22  and transmitter  24  are communicatively coupled via one or more optical wavelengths, where each wavelength (color) is a communications path. In one embodiment, receiver  22  and transmitter  24  are communicatively coupled via magnetic signals. In one embodiment, receiver  22  and transmitter  24  are communicatively coupled via pressure signals. 
         [0027]    In one embodiment, receiver  22  transmits the request via one communications path and transmitter  24  transmits the reply signal via the same communications path. In one embodiment, receiver  22  transmits the request via a first communications path and transmitter  24  transmits the reply signal via a second communications path. 
         [0028]    Receiver  22  and transmitter  24  communicate to send a request signal from receiver  22  to transmitter  24  and a reply signal from transmitter  24  to receiver  22 . In other embodiments, receiver  22  is configured to send a request signal from receiver  22  to transmitter  24  and a reply signal from receiver  22  to transmitter  24 , and transmitter  24  is configured to send a request signal from transmitter  24  to receiver  22  and a reply signal from transmitter  24  to receiver  22 . 
         [0029]    System  20  provides data communications between receiver  22  and transmitter  24  via a single communications path, such as one conductive line, or two communication paths, such as two conductive lines. These data communications have a high tolerance to time base differences between receiver  22  and transmitter  24 . Also, the request signal and the synchronization signal provide synchronization of the data communications and the request signal provides for the transmission of commands and/or data from receiver  22  to transmitter  24 . In addition, the request signal can include transmitter identifications that can be used in communications from a receiver to multiple transmitters, i.e. bus ability. 
         [0030]      FIG. 2  is a block diagram illustrating a request signal  50  and a reply signal  52  in one embodiment of system  20 . Reply signal  52  includes a synchronization signal  54  and data signals  56 . Synchronization signal  54  is a time base signal that indicates the time base of transmitter  24 . Each of the data signals  56  is correlated to the time base indicated via synchronization signal  54 . 
         [0031]    Receiver  22  transmits request signal  50  to transmitter  24  via one of the communication paths  26  and transmitter  24  transmits reply signal  52  to receiver  22  via one of the communication paths  26 . In response to a trigger signal at  58  in request signal  50 , transmitter  24  starts synchronization signal  54 . After reaching a pre-determined internal count value, transmitter  24  transmits a trailing edge at  60  in synchronization signal  54 . The length of synchronization signal  54 , from trigger signal  58  to trailing edge  60 , indicates the time base or clocking speed of transmitter  24 . In one embodiment, transmitter  24  uses the indicated time base to transmit data signals  56 , which correlates data signals  56  to the time base indicated by synchronization signal  54 . 
         [0032]    Receiver  22  transmits the remainder of request signal  50  after trigger signal  58 . The remainder of request signal  50  includes any commands and/or data to be transmitted to transmitter  24 , such as transmitter identification values, data request parameters such as a sensor measurement range, configurable parameters such as a relay turn-on/off time, and commands such as a self-test signal, a wake-up signal, a power down signal, a send data and remain powered-up signal, or a send data and power down signal. Request signal  50  overlaps in time at least a portion of synchronization signal  54  and if receiver  22  and transmitter  24  transmit via the same communications path, a trailing edge at  62  in request signal  50  occurs before the trailing edge  60  of synchronization signal  54  is transmitted via transmitter  24  on the same communications path. If receiver  22  and transmitter  24  transmit via different communication paths, the trailing edge  62  of request signal  50  can occur before or after the trailing edge  60  of synchronization signal  54  is transmitted via transmitter  24 . 
         [0033]    In one embodiment, receiver  22  is electrically coupled to transmitter  24  via one or more conductive lines and receiver  22  transmits request signal  50  on a first conductive line via voltage signals, such as voltage pulses or voltage bursts. Voltage signals on the first conductive line is a communications path. Request signal information is coded into the amplitude and/or length of the voltage pulses or coded into the amplitude, length, and/or frequency of the voltage bursts. Transmitter  24  transmits reply signal  52  via voltage signals, such as a pulse width modulated voltage signal, voltage pulses, or voltage bursts. Where leading and trailing edge information of synchronization signal  54  and data signals  56  are coded into the amplitude and/or length of the voltage pulses or the amplitude, length, and/or frequency of the voltage bursts. Receiver  22  and transmitter  24  generate the voltage signals via suitable circuitry, such as level-switching power stages, operational amplifiers, resistor networks, or open-drain/open-collector interfaces including pull-ups. Also, receiver  22  and transmitter  24  receive the voltage signals via suitable circuitry, such as window-detectors, schmitt-triggers, or open-drain/open-collector interfaces including pull-ups. If transmitter  24  transmits reply signal  52  via the first conductive line, request signal  50  and reply signal  52  share the same communications path and request signal  50  ends before the trailing edge  60  of synchronization signal  54 . If transmitter  24  transmits reply signal  52  via a second conductive line, request signal  50  and reply signal  52  do not share the same communications path and request signal  50  can end before or after the trailing edge  60  of synchronization signal  54 . 
         [0034]    In one embodiment, receiver  22  is electrically coupled to transmitter  24  via a conductive line and receiver  22  transmits request signal  50  on the conductive line via voltage signals, such as voltage pulses or voltage bursts. The voltage signals on the conductive line are a first communications path. Request signal information is coded into the amplitude and/or length of the voltage pulses or coded into the amplitude, length, and/or frequency of the voltage bursts. Transmitter  24  transmits reply signal  52  via current signals, such as current pulses or current bursts, where leading and trailing edge information of synchronization signal  54  and data signals  56  are coded into the amplitude and/or length of the current pulses or the amplitude, length, and/or frequency of the current bursts. The current pulses on the conductive line are a second communications path, such that request signal  50  and reply signal  52  do not share the same communications path and request signal  50  can end before or after the trailing edge  60  of synchronization signal  54 . 
         [0035]    In one embodiment, receiver  22  is communicatively coupled to transmitter  24  via antennae and one or more RF frequencies and receiver  22  transmits request signal  50  via a first RF frequency. The first RF frequency is a first communications path and request signal  50  is coded into the amplitude, length, and/or frequency of the RF signal or coded into the frequency/modulation factor, length, or amplitude of an RF modulated signal. Transmitter  24  transmits reply signal  52  via an RF frequency, where leading and trailing edges of synchronization signal  54  and data signals  56  are coded into the amplitude, length, and/or frequency of the RF signal or coded into the frequency/modulation factor, length, or amplitude of an RF modulated signal. If transmitter  24  transmits reply signal  52  via the first RF frequency, request signal  50  and reply signal  52  share the same communications path and request signal  50  ends before the trailing edge  60  of synchronization signal  54 . If transmitter  24  transmits reply signal  52  via a second RF frequency, request signal  50  and reply signal  52  do not share the same communications path and request signal  50  can end before or after the trailing edge  60  of synchronization signal  54 . 
         [0036]    In one embodiment, receiver  22  is communicatively coupled to transmitter  24  via an optical coupling, such as LED&#39;s or glass fibre, and one or more wavelengths (color). Receiver  22  transmits request signal  50  via a first wavelength, which is one communications path. Request signal  50  is coded into the amplitude, length, intensity, and/or burst frequency of the optical signal. Transmitter  24  transmits reply signal  52  via an optical wavelength, where leading and trailing edges of synchronization signal  54  and data signals  56  are coded into the amplitude, length, intensity, and/or burst frequency of the optical signal. If transmitter  24  transmits reply signal  52  via the first wavelength, request signal  50  and reply signal  52  share the same communications path and request signal  50  ends before the trailing edge  60  of synchronization signal  54 . If transmitter  24  transmits reply signal  52  via a second wavelength, request signal  50  and reply signal  52  do not share the same communications path and request signal  50  can end before or after the trailing edge  60  of synchronization signal  54 . 
         [0037]    In one embodiment, receiver  22  is communicatively coupled to transmitter  24  via a magnetic coupling, such as a coil, Receiver  22  transmits request signal  50  via the magnetic coupling, which is one communications path. Request signal  50  is coded into the amplitude, length, intensity, and/or frequency of the magnetic signal. Transmitter  24  transmits reply signal  52  via the magnetic coupling, where leading and trailing edges of synchronization signal  54  and data signals  56  are coded into the amplitude, length, intensity, and/or frequency of the magnetic signal. Request signal  50  and reply signal  52  share the same communications path and request signal  50  ends before the trailing edge  60  of synchronization signal  54 . 
         [0038]    In one embodiment, receiver  22  is communicatively coupled to transmitter  24  via a pressure coupling, such as piezo actor/sensor combinations or loudspeaker/microphone combinations. Receiver  22  transmits request signal  50  via the pressure coupling, which is one communications path. Request signal  50  is coded into the amplitude, length, intensity, and/or frequency of the pressure pulse signal. Transmitter  24  transmits reply signal  52  via the pressure coupling, where leading and trailing edges of synchronization signal  54  and data signals  56  are coded into the amplitude, length, intensity, and/or frequency of the pressure pulse signal. Request signal  50  and reply signal  52  share the same communications path and request signal  50  ends before the trailing edge  60  of synchronization signal  54 . 
         [0039]    In other embodiments, receiver  22  and transmitter  24  are suitably communicatively coupled. If they share the same communications channel or path, request signal  50  ends before the trailing edge  60  of synchronization signal  54 . If they do not share the same communications channel or path, request signal  50  ends before or after the trailing edge  60  of synchronization signal  54 . 
         [0040]    In another embodiment of system  20 , the synchronization signal is transmitted between data signals. Transmitter  24  starts transmitting data signals in response to a trigger signal in the request signal. Next, transmitter  24  transmits a synchronization signal and the remainder of the data signals. Some of the data signals are received and stored in receiver  22  prior to receiving the synchronization signal. The stored data signals are decoded after the synchronization signal is received from transmitter  24 . Also, at least a portion of the request signal overlaps in time at least a portion of the reply signal and one or more data signals. 
         [0041]    In another embodiment of system  20 , the synchronization signal is transmitted after the data signals. Transmitter  24  starts transmitting data signals in response to a trigger signal in the request signal. After transmitting the data signals, transmitter  24  transmits a synchronization signal. The data signals are received and stored in receiver  22  and decoded after the synchronization signal is received from transmitter  24 . Also, at least a portion of the request signal overlaps in time at least a portion of the reply signal and one or more data signals. 
         [0042]      FIG. 3  is a diagram illustrating a reply signal  70  that is transmitted via one embodiment of transmitter  24 . Reply signal  70  includes synchronization signal  72 , data signal D 1  at  74 , data signal D 2  at  76 , and data signal D 3  at  78 . The data signals D 1  at  74 , D 2  at  76 , and D 3  at  78  include transmitter information, such as transmitter status, data, and checksum information. Each of the data signals D 1  at  74 , D 2  at  76 , and D 3  at  78  represents one or more data bits. Synchronization signal  72  provides a reference time tREF at  72  that indicates the time base of transmitter  24 . Each of the data signal times tD 1  at  74 , tD 2  at  76 , and tD 3  at  78  correlates to reference time tREF at  72 . In one embodiment, each of the data signals D 1  at  74 , D 2  at  76 , and D 3  at  78  represents a nibble of data, i.e. four data bits. 
         [0043]    Receiver  22  transmits a request signal (not shown) to transmitter  24  via one of the communication paths  26 . In response to a trigger signal in the request signal, transmitter  24  provides a falling edge signal at  80  and a rising edge signal at  82  in synchronization signal  72 . After reaching a reference count, transmitter  24  transmits a trailing falling edge signal at  84 . The length of synchronization signal  72 , from the falling edge at  80  to the falling edge at  84  is reference time tREF at  72 . Synchronization signal  72  is made to be distinguishable from each of the data signals D 1  at  74 , D 2  at  76 , and D 3  at  78 . In one embodiment, reference time tREF at  72  is the longest pulse width that can be provided via transmitter  24 . In one embodiment, reference time tREF at  72  is the shortest pulse width that can be provided via transmitter  24 . 
         [0044]    Receiver  22  transmits the remainder of the request signal after the falling edge at  80 . The remainder of the request signal includes any commands and/or data to be transmitted to transmitter  24 . The request signal overlaps in time at least a portion of synchronization signal  72 . If receiver  22  and transmitter  24  transmit via the same communications path, the trailing edge of the request signal occurs before the trailing falling edge at  84 . If receiver  22  and transmitter  24  transmit via different communication paths, the trailing edge of the request signal can occur before or after the trailing falling edge at  84 . In one embodiment, receiver  22  and transmitter  24  are electrically coupled via one conductive line and they communicate via open drain/collector transistors with pull-up resistors, where the remainder of the request signal is transmitted after the rising edge at  82  and before the falling edge at  84 . 
         [0045]    Transmitter  24  transmits data signal Dl at  74 , data signal D 2  at  76 , and data signal D 3  at  78 . The length of data signal D 1  at  74 , from the falling edge at  84  to a falling edge at  86 , is data signal time tD 1  at  74 . The length of data signal D 2  at  76 , from the falling edge at  86  to a falling edge at  88 , is data signal time tD 2  at  76 . The length of data signal D 3  at  78 , from the falling edge at  88  to a falling edge at  90 , is data signal time tD 3  at  78 . Each of the data signal times tD 1  at  74 , tD 2  at  76 , and tD 3  at  78  correlates to reference time tREF at  72 . 
         [0046]    In other embodiments, synchronization signal  72  is transmitted between or after data signals, such as data signals D 1  at  74 , D 2  at  76 , and D 3  at  78 . The data signals received before synchronization signal  72  are stored and decoded after receiving synchronization signal  72 . Also, at least a portion of the request signal overlaps in time at least a portion of the reply signal and one or more of the data signals. 
         [0047]      FIG. 4  is a diagram illustrating one embodiment of an electrical system  100 , which includes a controller  102 , a first sensor  104 , and a second sensor  106 . Controller  102  is electrically coupled to each of the sensors  104  and  106  via a 3-wire connection. Controller  102  is electrically coupled to first sensor  104  and second sensor  106  via VDD power supply line  108 , data line  110 , and a reference line, such as ground line  112 . In one embodiment, system  100  is part of an automobile&#39;s electrical system. In other embodiments, controller  102  is electrically coupled to any suitable number of sensors. 
         [0048]    Controller  102  communicates with first sensor  104  and second sensor  106  via open-drain/open-collector interfaces including one or more pull-up resistors. For example, system  100  includes pull-up resistor  114  that has a first end electrically coupled to power supply line  108  and a second end electrically coupled to data line  110 , and controller  102  includes an open-drain transistor  116  that has one end of its drain-source path electrically coupled to data line  110  and the other end electrically coupled to ground line  112 . Controller  102  and each of the first and second sensors  104  and  106  share a single communications path that is communicating via voltage signals on data line  110 . 
         [0049]    Controller  102  transmits a request signal that is received by the first and second sensors  104  and  106  via data line  110 . The request signal includes a trigger signal and a sensor identification signal that selects one of the first and second sensors  104  and  106 . In addition, the remainder of the request signal includes any other commands and/or data to be transmitted to the selected sensor, such as data request parameters such as a sensor measurement range, configurable parameters such as a relay turn-on/off time, and commands such as a self-test signal, a wake-up signal, a power down signal, a send data and remain powered-up signal, or a send data and power down signal. Controller  102  and each of the first and second sensors  104  and  106  share a single communications path such that the request signal ends before the trailing edge of the synchronization signal. 
         [0050]    The first and second sensors  104  and  106  receive the request signal including the trigger signal and the sensor identification signal. One of the first and second sensors  104  and  106  is selected via the sensor identification signal and the selected sensor transmits a reply signal via data line  110 . In one embodiment, the reply signal is similar to reply signal  70  of  FIG. 3 . 
         [0051]    The reply signal includes a synchronization signal and data signals. The data signals include sensor information, such as sensor status, sensor data, and checksum information. The length of the synchronization signal provides a reference time that indicates the time base of the selected sensor. Each of the data signal lengths correlates to the reference time. In one embodiment, each of the data signals represents a nibble of data, i.e. four data bits. 
         [0052]    The request signal and the synchronization signal overlap in time, where at least a portion of the request signal occurs at the same time as at least a portion of the synchronization signal. In response to the trigger signal, the selected sensor starts the synchronization signal and after reaching a reference count transmits the trailing falling edge of the synchronization signal to mark the end of the synchronization signal. The request signal ends before the trailing falling edge of the synchronization signal. 
         [0053]    In one embodiment, the length of the synchronization signal is measured from the trigger signal to the trailing falling edge of the synchronization signal. In one embodiment, the selected sensor transmits a falling edge followed by a rising edge to start the synchronization signal. In one embodiment, the selected sensor transmits a high voltage value at the start of the synchronization signal and the length of the synchronization signal is measured from the trigger signal to the trailing falling edge of the synchronization signal. In one embodiment, the length of the synchronization signal is the longest pulse that can be provided via the selected sensor. 
         [0054]    In another embodiment, a data signal is transmitted first in the reply signal, where at least a portion of the request signal occurs at the same time as at least a portion of the data signal. In response to the trigger signal, the selected sensor starts the data signal and after reaching an end count for the data signal transmits the trailing falling edge of the data signal. The request signal ends before the trailing falling edge of the data signal. 
         [0055]    Controller  102  receives the synchronization signal and measures the length of the synchronization signal to obtain the time base of the selected sensor. Based on the received time base, controller  102  recovers data from the data signals via measuring the length of the data signals and comparing the measured length to the received time base. 
         [0056]    In other embodiments, controller  102  transmits the request signal via VDD power supply line  108  and first and second sensors  104  and  106  transmit reply signals via data line  108 . 
         [0057]      FIG. 5  is a timing diagram illustrating the operation of one embodiment of system  100  of  FIG. 4 . Controller  102  communicates with first and second sensors  104  and  106  via data line  110 . In one communication sequence, controller  102  selects one of the first and second sensors  104  and  106  and the selected sensor provides sensor functions at  130 . Controller  102  and the selected sensor transmit data line signal  132  via data line  110 . Data line signal  132  is further described in the logical description at  134 . 
         [0058]    At  136 , first and second sensors  104  and  106  are idle and controller  102  transmits a request signal that includes a trigger signal, a sensor identification signal, and a sensor range signal. The falling edge at  138  in data line signal  132  is the trigger signal. The length tID at  140  of the low voltage level following the falling edge at  138  and ending at a rising edge at  142  is the sensor identification signal. The length tR at  144  of the low voltage level from the falling edge at  146  to a rising edge at  148  is the sensor range signal. 
         [0059]    In response to the trigger signal falling edge at  138 , first and second sensors  104  and  106  start transmitting synchronization signals at  150 . In one embodiment, each of the synchronization signals includes a falling edge followed by a rising edge to start the synchronization signal. In one embodiment, each of the synchronization signals includes a high voltage level at the start of the synchronization signal. 
         [0060]    At  152 , each of the first and second sensors  104  and  106  checks the low voltage level time tID at  140  of the identification signal. The selected sensor continues on to check the low voltage level time tR at  144  of the sensor range signal, which indicates the sensor range to use in data transmissions. Next, the selected sensor transmits a falling edge at  154  that ends the synchronization signal of the selected sensor and the synchronization period  156 . 
         [0061]    Controller  102  receives the falling edge at  154  of the synchronization signal and obtains the time base of the selected sensor. In one embodiment, the length of the synchronization signal is measured from the trigger signal falling edge at  138  to the trailing falling edge at  154  of the synchronization signal. 
         [0062]    The selected sensor transmits data signals at  158 , where each of the data signals has a length that indicates the bit value of the data signal. The first data signal at  160  is a status signal that indicates the status of the selected sensor. The length of the status signal at  160  begins with the falling edge at  154  and ends with a falling edge at  162 . The length of the second data signal DATA 2  at  164  begins with the falling edge at  162  and ends with a falling edge at  166 , and so on, up to the final data signal DATAx at  168  and a checksum signal at  170 . The length of the checksum signal at  170  begins with a falling edge at  172  and ends with a falling edge at  174 . At  176 , a zero signal begins with the falling edge at  174  and ends at a high voltage level. The data signals end at  178  and the selected sensor is idle at  180 . 
         [0063]    Controller  102  receives the data signals at  158  via data line signal  132 . Controller  102  measures the length of each of the data signals  158  from one falling edge to the next falling. Based on the received time base, controller  102  recovers the data bit values of each of the data signals  158 . 
         [0064]    System  100  provides data communications between controller  102  and first and second sensors  104  and  106  via the single communications path of data line  110 . The data communications have a high tolerance to time base differences between controller  102  and the first and second sensors  104  and  106 . Also, the request signal and the synchronization signal provide synchronization of the data communications and the request signal provides for the transmission of commands and/or data from controller  102  to first and second sensors  104  and  106 . In addition, the request signal includes sensor identification signals that provide bus ability. 
         [0065]    Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.