Modbus RTU Slave: How to Read and Write Controller Output CO

1. Scenario Description

• Device: xArm Controller (AC1320 or later, AC8520 or later)
• Firmware: V2.7.104 or later
• Communication: Modbus RTU
• Device Role: Slave
• Target Function:
  • CO0 -> Low level
  • CO1 -> High level
  • CO2 -> High level
  • CO3 -> Low level

2. Mapping Between Coils and CO

Modbus Coil Address	Controller CO	Description
0000	CO0	Controller Output 0
0001	CO1	Controller Output 1
0002	CO2	Controller Output 2
0003	CO3	Controller Output 3

3. Modbus RTU Command Examples (Function Code 0x0F)

3.1 Setting CO

Raw Command Frame (HEX)

01 0F 00 00 00 04 01 06 BE 94

Command Structure Breakdown

Slave Address: 01 (1)
Function Code: 0F
Start Address: 00 00 (0000)
Number of Coils: 00 04 (4)
Byte Count: 01 (1)
Data Field:
  Byte 0: 06 (bit0:0, bit1:1, bit2:1, bit3:0)
CRC: BE 94

Response Frame (HEX)

01 0F 00 00 00 04 54 08

Command Structure Breakdown

Slave Address: 01 (1)
Function Code: 0F
Start Address: 00 00 (0)
Number of Coils: 00 04 (4)
CRC: 54 08

3.2 Reading CO

Raw Command Frame (HEX)

01 01 00 00 00 04 3D C9

Command Structure Breakdown

Slave Address: 01 (1)
Function Code: 01
Start Address: 00 00 (0000)
Quantity: 00 04 (4)
CRC: 3D C9

Response Frame (HEX)

01 01 01 06 D1 8A

Command Structure Breakdown

Slave Address: 01 (1)
Function Code: 01
Byte Count: 01 (1)
Data Field:
  Byte 0: 06 (bit0:0, bit1:1, bit2:1, bit3:0)
CRC: D1 8A