Modbus Protocol - GE Multilin 850 Communications Manual

GE
Grid Solutions
8 Series Protective Relay Platform
Chapter 11: Modbus Protocol
8 SERIES PROTECTIVE RELAY PLATFORM – COMMUNICATIONS GUIDE

Modbus Protocol

All Ethernet ports and serial communication ports support the Modbus protocol. The only
exception is if the serial port has been configured for DNP or IEC 60870-5-103 operation
(see descriptions below). This allows the EnerVista 8 Series Setup software (which is a
Modbus master application) to communicate to the 8 Series relay.
The 8 Series relay implements a subset of the Modicon Modbus RTU serial communication
standard. The Modbus protocol is hardware-independent. That is, the physical layer can be
any of a variety of standard hardware configurations. This includes USB, RS485, fiber
optics, etc. Modbus is a single master / multiple slave type of protocol suitable for a multi-
drop configuration.
The 8 Series relay is always a Modbus slave with a valid slave address range 1 to 254.
DATA FRAME FORMAT AND DATA RATE
One data frame of an asynchronous transmission to or from an 8 Series relay typically
consists of 1 start bit, 8 data bits, and 1 stop bit. This produces a 10-bit data frame. This is
important for transmission through modems at high bit rates. Modbus protocol can be
implemented at any standard communication speed. The 8 Series relay supports
operation at 9600, 19200, 38400, 57600, and 115200 bps baud rate. The USB interface
supports ModBus TCP/IP.
FUNCTION CODE SUPPORTED
The following functions are supported by the 8 Series relay:
• FUNCTION CODE 03H - Read Setpoints
• FUNCTION CODE 04H - Read Actual Values
• FUNCTION CODE 05H - Execute Operation
• FUNCTION CODE 06H - Store Single Setpoint
• FUNCTION CODE 07H - Read Device Status
• FUNCTION CODE 08H - Loopback Test
• FUNCTION CODE 10H - Store Multiple Setpoints
• FUNCTION CODE 42H - Group Settings Read
• FUNCTION CODE 43H - Group Settings Write
When a ModBus master such as the EnerVista 8 Series Setup software communicates to
the 8 Series relay over Ethernet, the 8 Series relay slave address, TCP port number and the
8 Series relay IP address for the associated port must be configured and are also
configured within the Master for this device. The default ModBus TCP port number is 502.
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