COMMUNICATIONS GUIDE
MODBUS FUNCTIONS
469 MOTOR MANAGEMENT RELAY – COMMUNICATIONS GUIDE
5
Modbus Functions
Supported Functions
The following functions are supported by the 469:
Modbus Function Code 01: Read Relay Coil
Modbus Function Code 02: Read Digital Input Status
Modbus Function Code 03: Read Setpoints and Actual Values
Modbus Function Code 04: Read Setpoints and Actual Values
Modbus Function Code 05: Execute Operation
Modbus Function Code 06: Store Single Setpoint
Modbus Function Code 07: Read Device Status
Modbus Function Code 08: Loopback Test
Modbus Function Code 16: Store Multiple Setpoints
Read Relay Coil / Digital Input Status
Modbus implementation: Read Coil and Input Status
469 Implementation: Read Relay Coil and Digital Input Status
For the 469 implementation of Modbus, these commands can be used to read Relay Coil
Status or Digital Input Status.
MESSAGE FORMAT AND EXAMPLE, FUNCTION 01:
The standard implementation requires the following: slave address (one byte), function
code (one byte), starting relay coil (two bytes), number of coils to read (two bytes), and CRC
(two bytes). The slave response is the slave address (one byte), function code (one byte),
relay coil mask byte count (one byte; always 01 since only six relay coils), bit mask
indicating the status of requested relay coils (one byte), and CRC (two bytes).
Request slave 11 to respond with status of relay coil 3 to 5:
Relay
Status
1 TRIP
Energized
2 AUXILIARY
De-energized
3 AUXILIARY
De-energized
4 ALARM
De-energized
5 BLOCK START
Energized
6 SERVCE
Energized
Bit Mask
0011 0001 (0
×
31)
Master Transmission
Bytes
Example
Description
Slave Address
1
0B
message for slave 11
Function Code
1
01
read relay coil status
Starting Relay Coil
2
00 03
starting relay coil 3
Number of Relays
2
00 03
3 relay coils (relays 3 AUXILIARY,
4 AUXILIARY, and 5 BLOCK START)
CRC
2
8C A1
computed CRC error code
Slave Response
Bytes
Example
Description
Slave Address
1
0B
message from slave 11