Function Code 05H - GE 345 Communications Manual

MODBUS FUNCTIONS

Function Code 05H

1–172
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
MASTER TRANSMISSION
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS
NUMBER OF ACTUAL VALUES
CRC
SLAVE RESPONSE
SLAVE ADDRESS
FUNCTION CODE
BYTE COUNT
DATA (see definition above)
CRC
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
SLAVE ADDRESS
FUNCTION CODE
OPERATION CODE
CODE VALUE
CRC
SLAVE RESPONSE
SLAVE ADDRESS
FUNCTION CODE
OPERATION CODE
CODE VALUE
CRC
CHAPTER 1: COMMUNICATIONS GUIDE
BYTES EXAMPLE
1 11
1 04
2 00 08
2 00 01
2 B2 98
BYTES EXAMPLE
1 11
1 04
1 02
2 00 00
2 78 F3
BYTES EXAMPLE
1 11
1 05
2 00 01
2 FF 00
2 DF 6A
BYTES EXAMPLE
1 11
1 05
2 00 01
2 FF 00
2 DF 6A
345 TRANSFORMER PROTECTION SYSTEM – COMMUNICATIONS GUIDE
DESCRIPTION
message for slave 17
read registers
data starting at 0008
1 register = 2 bytes
CRC error code
DESCRIPTION
message from slave
17
read registers
1 register = 2 bytes
value in address
0008
CRC error code
DESCRIPTION
message for slave 17
execute operation
operation code 1
perform function
CRC error code
DESCRIPTION
message from slave
17
execute operation
operation code 1
perform function
CRC error code