How to set/get controller analog output value via Modbus TCP?

Holding Registers:

• function code: 0x03(read), 0x06(write)
• registers: 0x03

Example to Read AO0&AO1

Send: 00 01 00 00 00 06 01 03 00 03 00 02
Respond: 00 01 00 00 00 07 01 03 04 13 86 0B B6

Send:

• 00 01 00 00: fixed
• 00 06: data length
• 01: ID, fixed
• 03: function code
• 00 03: register address
• 00 02: read 2 register

Respond:

• 13 86: 4998/1000 ≈ 5V
• 0B B6: 2998/1000 ≈ 3V

Example to Set AO1 to 1V

Send: 00 01 00 00 00 06 01 06 00 04 03 E8
Respond: 00 01 00 00 00 06 01 06 00 04 03 E8

Send:

• 00 01 00 00: fixed
• 00 06: data length
• 01: ID, fixed
• 06: function code
• 00 04: register address of AO1
• 03 E8: 1000/1000 =1V