Abstract:
An interface monitor is connected with a LAN that is formatted with an RS-485 protocol and which is interconnected with a plurality of electrical distribution devices. The monitor includes a socket connection for receiving an RS-232 plug from a PC and software logic for interpreting between the RS-232 and RS-485 formats. The PC is enabled for communicating with each one of the electrical distribution devices.

Description:
BACKGROUND OF THE INVENTION 
     The interconnection of a number of electrical equipment for supervisory control and data acquisition is described within U.S. patent application Ser. No. 08/628,533 filed Apr. 3, 1996 entitled &#34;Dynamic Data Exchange Server Simulator&#34;. The electrical equipment is interconnected within a LAN utilizing a Modbus protocol which is a trademark of New Modicon Inc. for RS-485 data format. 
     When a personal computer is to be connected with the LAN to interrogate the status of any of the equipment, the computer modem port is temporarily connected with the LAN by means of the modem port that is adapted for receiving data in RS-232 data format. Additional software must be included within the personal computer and the connector cable must be adapted for direct connection with the LAN. 
     One example of a method for interrogating a circuit breaker operating within a LAN is found in U.S. Pat. No. 5,596,473 entitled &#34;Electrical Switches With Current Protection Interfaced With A Remote Station and A Portable Local Unit&#34;. 
     Various modules are commercially available for connecting between RS-232 data format and proprietary protocol used within most LAN systems as described within the following U.S. patents. 
     U.S. Pat. No. 5,127,090 entitled &#34;Map Interface Unit (MAP) for Industrial Programmable Logic Controllers&#34; describes a manufacturing automation protocol (MAP) interface unit that couples a LAN, connecting with programmable logic controllers, to a MAP network. 
     U.S. Pat. No. 5,245,703 entitled &#34;Data Processing System With Multiple Communication Buses and Protocols&#34; discloses an interface unit for connecting between internal and external communication buses having different protocols. 
     U.S. Pat. No. 5,355,365 entitled &#34;Intelligent Local Area Network Modem Mode&#34; describes a LAN modem node that allows PC&#39;s on the LAN to communicate with off-LAN PC&#39;s, printers and other local area networks. 
     When there is a need for a host PC to communicate with any of the electrical equipment on the LAN, as described within the aforementioned U.S. patent application Ser. No. 08/628,533, it would be convenient to interpose a monitor unit having capacity to receive both RS-232 configured and RS-485 configured plug sockets along with the capacity to translate between the associated RS-232 and RS-485 protocols. 
     One purpose of the invention, accordingly, is to provide a stand-alone monitor unit that allows external connection with a dedicated LAN by use of standard PC connector cables. 
     SUMMARY OF THE INVENTION 
     An interface monitor is connected with a LAN that is formatted with an RS-485 protocol and which is interconnected with a plurality of electrical devices. The monitor includes a socket connection for receiving an RS-232 plug from a PC and includes sufficient software logic for interpreting between the RS-232 and RS-485 formats. The PC is enabled for communicating with each one of the electrical devices. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is schematic representation of the interface monitor connection between a PC and LAN according to the invention; 
     FIG. 2 is an enlarged schematic representation of the components within the representation depicted in FIG. 1; and 
     FIG. 3 is an enlarges schematic representation of the components within the monitor unit of FIG. 2; 
     FIG. 4 is a flow chart representation of the algorithms contained within the interface monitor of FIGS. 1 and 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIG. 1, a number of distributed electrical metering and control devices 11-14, such as relays, meters, circuit breakers and the like described in the aforementioned U.S. patent application Ser. No. 08/628,533, are interconnected by means of a cable connector 15 with a LAN 10 containing RS-485 protocol. A good example of a circuit breaker having such communication facility is found in U.S. Pat. No. 4,675,481 entitled &#34;Circuit Breaker and Protective Relay Unit&#34;. When a PC 18 such as an IBM 350-P75 is required to address any of the devices to request status and other information, the PC is connected by means of a cable connector 19 with a monitor unit 17 in the form of an enclosure that contains a plurality of circuit components which will be described later with reference to FIG. 3. The monitor 17 connects with the LAN by means of a cable connector 16. Since the cable connector 19 is removably-connectable with the monitor, various PC&#39;s can be connected at different times to access the LAN without requiring any modification to the PC or the monitor to make the connection. 
     This feature is best understood by now referring to FIG. 2 wherein the PC 18 is shown having an RS-232 socket or port 20 arranged on a rear surface thereof. The enclosure 9 that defines the monitor 17 includes both an RS-232 port 30 for receiving the cable connector 19 from the PC 18 as well as an RS-485 port 31 for receiving the cable 32 that connects with the LAN 10. The electrical device 11, consisting of a circuit breaker, meter or the like, connects with the LAN 10 by means of the cable 15 and the RS-485 port 33. Communication between the RS-232 port 30 and the RS-485 port 31 is made by a conversion algorithm resident within the monitor microprocessor described earlier. It is thus seen that at different times, different PC&#39;s 18 can communicate with any number of devices 11 by the use of a single monitor 17, in accordance with the teachings of the invention. 
     As shown in FIG. 3, the monitor 17 includes a CPU in the form of a microprocessor 35 connecting with a display driver 46 over rail 42 and with a keyboard controller 47 over rail 40 to provide external keypad and display facility. The microprocessor connects with a RAM 36 over rail 44 and the RAM contains a program for converting RS-232 protocol resident in the PC modem with the protocol employed within the LAN 10 of FIG. 1 in the manner to be described below. To provide timing facility, the microprocessor connects with a clock 37 over rail 45. In further accordance with the teachings of the invention, the RS-232 port 30 includes a Universal Address Radio Transceiver &#34;UART&#34; 39 such as an SP type 16C550 configured for RS-232 communications and connects with the microprocessor over rail 41. The RS-485 port 31 includes a similar UART 38 configured for RS-485 communication. As shown earlier, in FIG. 2, the PC 18 connects with the RS-232 port 20 and the LAN 10 connects with the RS-485 port 31. The conversion program within the RAM 36 operates in the following manner. When a message is received on the RS-232 port 30, the UART 39 passes a byte to the microprocessor port 1 over rail 41. The microprocessor 35 then copies the message to port 2, which transmits the message to the RS-485 port 31 over rail 43. When a message is received at the RS-485 port 31, the UART 38 passes a byte to the microprocessor port 2 over rail 43. The microprocessor 35 then copies the message to port 1, which transmits the message to the RS-232 port 30 over rail 41. 
     To provide address between any of the electrical devices 11-14 of FIG. 1, the Flow Chart 21 depicted in FIG. 4 is employed as follows. Auto detection (22) provides a means of self-configuring by scanning the LAN for all devices 11-14. The auto detection program resident in the monitor 17 (FIG. 2) scans all device addresses and waits for a response from the device. By inspecting the response received, the device characteristics can be determined. Absence of a device at a particular address is determined when a time-out condition occurs. Two retries are attempted to determine if a device is at a given address. 
     When auto detection (22) is requested, the port configuration file is sent to the monitor to ensure that the ports 33 of FIG. 2 are set up properly. If the auto detection is successful, the devices found on the network are stored in a database file within the monitor and analyzed. Devices that match a device already stored in the database file are discarded. Devices that are not in the database file are added. Devices that are unknown are marked as unknown and added to the database file. Devices already in the database file are retained. When the database file is about to be saved, if unknown devices are present, indication is made that unknown devices exist and will be deleted. If any unknown devices exist at the time the database file is to be saved permanently, these devices are deleted. 
     The main form is displayed (23) on the PC screen upon startup of the Autodetection program allowing the PC operator to initialize the status structure (24) and the internal PC transmitter and receiver buffers (25). 
     The device scan process is started at a first baud rate(26) and messages are sent to each device address stored in the monitor data file at a first baud rate to determine if the address is correct. If the device fails to respond after two attempts (27), the baud rate is lowered by a defined increment and the request is repeated (28) until a response is received and until all the devices have been scanned (29, 30). 
     Another application of the monitor 17 shown in FIGS. 1 and 2 is to provide standby master control facility to the devices listed within the aforementioned U.S. patent application Ser. No. 08/628,533, in the event the master server becomes disabled. The monitor having acquired the function and location of all the devices within the LAN is then able to communicate with the devices to provide supervisory data acquisition and control function. 
     A monitor unit has herein been described for allowing access between a PC employing one communications protocol to access any one of a series of devices connected within a LAN having a different protocol.