CHAPTER 8: MODBUS FUNCTIONS FUNCTION CODE 08H
SR3 SERIES PROTECTIVE RELAY PLATFORM – COMMUNICATIONS GUIDE 8-11
Function Code 08H
Modbus Implementation: Loopback
Test 3 Series relay Implementation: Loopback Test
This function is used to test the integrity of the communication link. The 3 Series relay will
echo the request.
For example, consider a loopback test from slave 17:
Table 8-7: MASTER/SLAVE PACKET FORMAT FOR FUNCTION CODE 08H
Function Code 10H
Modbus Implementation: Preset Multiple Registers
3 Series relay Implementation: Store Multiple Setpoints
This function code allows multiple Setpoints to be stored into the 3 Series relay memory.
Modbus “registers” are 16-bit (two byte) values transmitted high order byte first. Thus all 3
Series relay
setpoints are sent as two bytes. The maximum number of Setpoints that can
be stored in one transmission is dependent on the slave device. Modbus allows up to a
maximum of 60 holding registers to be stored. The 3 Series relay
response to this function
code is to echo the slave address, function code, starting address, the number of Setpoints
stored, and the CRC.
For example, consider a request for slave 17 to store the value 00 02 to setpoint address 04
5C and the value 01 F4 to setpoint address 04 5D. After the transmission in this example is
complete, 3 Series relay
slave 17 will have the following setpoints information stored:
The master/slave packets have the following format:
MASTER TRANSMISSION BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message for slave 17
FUNCTION CODE 1 08 loopback test
DIAG CODE 2 00 00 must be 00 00
DATA 2 00 00 must be 00 00
CRC 2 E0 0B CRC error code
SLAVE RESPONSE BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message from slave
17
FUNCTION CODE 1 08 loopback test
DIAG CODE 2 00 00 must be 00 00
DATA 2 00 00 must be 00 00
CRC 2 E0 0B CRC error code
Address Data
04 5C 00 02
04 5D 01 F4
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