GE 869, Communications Manual

Page: 90 / 436

10-6 869 MOTOR PROTECTION SYSTEM – COMMUNICATIONS GUIDE
MODBUS PROTOCOL CHAPTER 10: MODBUS PROTOCOL
Table 10-12: Master Packet Format for Function Code 08H
Table 10-13: Slave Packet Format for Function Code 08H
Function Code 10H
Modbus Implementation: Preset Multiple Registers
869 Implementation: Store Multiple Setpoints
The function code allows multiple Setpoints to be stored into the 869 memory. Modbus
“registers” are 16-bit (two byte) values transmitted high order byte first. Thus all
869 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 869 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
045C and the value 01 F4 to setpoint address 04 5D. After the transmission in this example
is complete, 869 slave 17 will have the following setpoints information stored:
Table 10-14: Master Packet Format for Function Code 10H
Table 10-15: Slave Packet Format for Function Code 10H
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
MASTER TRANSMISSION BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message for slave 17
FUNCTION CODE 1 10 store setpoints
DATA STARTING ADDRESS 2 04 5C setpoint address 04 5C
NUMBER OF SETPOINTS 2 00 02 2 setpoints – 4 bytes total
BYTE COUNT 1 04 4 bytes of data
DATA 1 2 00 02 data for setpoint address 04 5C
DATA 2 2 01 F4 data for setpoint address 04 5D
CRC 2 31 11 CRC error code
SLAVE RESPONSE BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message from slave 17
FUNCTION CODE 1 10 store setpoints