GE 345 Communications Manual

1–172 345 TRANSFORMER PROTECTION SYSTEM – COMMUNICATIONS GUIDE
MODBUS FUNCTIONS CHAPTER 1: COMMUNICATIONS GUIDE
For the 345 implementation of Modbus, this function code can be used to read any actual
values (“input registers”). Input registers are 16 bit (two byte) values transmitted high order
byte first. Thus all 345 Actual Values are sent as two bytes. The maximum number of
registers that can be read in one transmission is 125.
The slave response to this function code is the slave address, function code, a count of the
data bytes to follow, the data itself and the CRC. Each data item is sent as a two byte
number with the high order byte sent first.
For example, request slave 17 to respond with 1 register starting at address 0008. For this
example the value in this register (0008) is 0000.
Table 34: MASTER/SLAVE PACKET FORMAT FOR FUNCTION CODE 04H
Function Code 05H
Modbus Implementation: Force Single Coil
345 Implementation: Execute Operation
This function code allows the master to request a 345 to perform specific command
operations.
For example, to request slave 17 to execute operation code 1 (reset), we have the following
master/slave packet format:
Table 35: MASTER/SLAVE PACKET FORMAT FOR FUNCTION CODE 05H
MASTER TRANSMISSION BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message for slave 17
FUNCTION CODE 1 04 read registers
DATA STARTING ADDRESS 2 00 08 data starting at 0008
NUMBER OF ACTUAL VALUES 2 00 01 1 register = 2 bytes
CRC 2 B2 98 CRC error code
SLAVE RESPONSE BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message from slave
17
FUNCTION CODE 1 04 read registers
BYTE COUNT 1 02 1 register = 2 bytes
DATA (see definition above) 2 00 00 value in address
0008
CRC 2 78 F3 CRC error code
MASTER TRANSMISSION BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message for slave 17
FUNCTION CODE 1 05 execute operation
OPERATION CODE 2 00 01 operation code 1
CODE VALUE 2 FF 00 perform function
CRC 2 DF 6A CRC error code
SLAVE RESPONSE BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message from slave
17
FUNCTION CODE 1 05 execute operation
OPERATION CODE 2 00 01 operation code 1
CODE VALUE 2 FF 00 perform function
CRC 2 DF 6A CRC error code

GE 345 Specifications

General

Brand	GE
Model	345
Category	Relays
Language	English