GE 869 Communications Manual page 90

MODBUS PROTOCOL
10-6
Table 10-12: Master Packet Format for Function Code 08H
MASTER TRANSMISSION
SLAVE ADDRESS
FUNCTION CODE
DIAG CODE
DATA
CRC
Table 10-13: Slave Packet Format for Function Code 08H
SLAVE RESPONSE
SLAVE ADDRESS
FUNCTION CODE
DIAG CODE
DATA
CRC
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:
Address
04 5C
04 5D
Table 10-14: Master Packet Format for Function Code 10H
MASTER TRANSMISSION
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS
NUMBER OF SETPOINTS
BYTE COUNT
DATA 1
DATA 2
CRC
Table 10-15: Slave Packet Format for Function Code 10H
SLAVE RESPONSE
SLAVE ADDRESS
FUNCTION CODE
BYTES EXAMPLE
1 11
1 08
2 00 00
2 00 00
2 E0 0B
BYTES EXAMPLE
1 11
1 08
2 00 00
2 00 00
2 E0 0B
Data
00 02
01 F4
BYTES EXAMPLE
1 11
1 10
2 04 5C
2 00 02
1 04
2 00 02
2 01 F4
2 31 11
BYTES EXAMPLE
1 11
1 10
869 MOTOR PROTECTION SYSTEM – COMMUNICATIONS GUIDE
CHAPTER 10: MODBUS PROTOCOL
DESCRIPTION
message for slave 17
loopback test
must be 00 00
must be 00 00
CRC error code
DESCRIPTION
message from slave 17
loopback test
must be 00 00
must be 00 00
CRC error code
DESCRIPTION
message for slave 17
store setpoints
setpoint address 04 5C
2 setpoints – 4 bytes total
4 bytes of data
data for setpoint address 04 5C
data for setpoint address 04 5D
CRC error code
DESCRIPTION
message from slave 17
store setpoints