16-
2
750/760 Feeder Management Relay
GE Power Management
16.2 PHYSICAL LAYER
16 COMMUNICATIONS
16
16.2 PHYSICAL LAYER
16.2.1 DESCRIPTION
Both the MODBUS and DNP protocols are hardware-independent so that the physical layer can be any of a
variety of standard hardware configurations including RS232, RS422, RS485, fiber optics, etc. The 750/760
includes a front panel RS232 port and two rear terminal RS485 ports, one of which can also be configured as
RS422. Data flow is half duplex in all configurations. See Chapter 3: INSTALLATION for details on wiring.
Each data byte is transmitted in an asynchronous format consisting of 1 start bit, 8 data bits, 1 stop bit, and
possibly 1 parity bit. This produces a 10 or 11 bit data frame. This is important for transmission through
modems at high bit rates (11 bit data frames are not supported by many modems at baud rates greater than
300).
The baud rate and parity are independently programmable for each communications port. Baud rates of 300,
1200, 2400, 4800, 9600, and 19200 are available. Even, odd, and no parity are available. See Section 8.2:
COMMUNICATIONS on page 8–2 for further details.
The master device in any system must know the address of the slave device with which it is to communicate.
The 750/760 will not act on a request from a master if the address in the request does not match the relay’s
slave address (unless the address is the broadcast address – see below).
A single setpoint selects the slave address used for all ports with the exception that for the front panel port the
relay will accept any address when the MODBUS protocol is used. The slave address is otherwise the same
regardless of the protocol in use, but note that the broadcast address is 0 for MODBUS and 65535 for DNP.
The relay recognizes and processes a master request (under conditions that are protocol-specific) if the broad-
cast address is used but never returns a response.
DNP may be used on, at most, one of the communications ports. Any port(s) not selected to use DNP will com-
municate using MODBUS. Setpoint
S1 RELAY SETUP / COMMUNICATIONS / DNP PORT
is used to select which port
will communicate using DNP.
The maximum time for a 750/760 relay to return a response to any (non-broadcast) master request will never
exceed 1 second.
Summary of Contents for 750
Page 2: ......
Page 4: ......
Page 124: ...8 14 750 760 Feeder Management Relay GE Power Management 8 12 INSTALLATION 8 S1 RELAY SETUP 8 ...
Page 488: ...A 4 750 760 Feeder Management Relay GE Power Management A 1 FIGURES AND TABLES APPENDIXA A ...
Page 492: ...C 2 750 760 Feeder Management Relay GE Power Management C 1 WARRANTY INFORMATION APPENDIXC C ...
Page 502: ...x 750 760 Feeder Management Relay GE Power Management INDEX ...
Page 503: ...GE Power Management 750 760 Feeder Management Relay NOTES ...