Can't read from a Micro820 Modbus Server / Slave

[bill1995]

Hello,

I set up my Micro820 with a basic mapping. When I try to run a script to read the addresses I get errors for illegal addresses.

• Connected to Modbus Server
• _IO_EM_DO_01: OFF
• _IO_EM_DO_02: OFF
• _IO_EM_DO_03: OFF
• _IO_EM_DO_04: ON
• Error reading _IO_EM_DI_01: Exception Response(130, 2, IllegalAddress)
• Error reading _IO_EM_DI_02: Exception Response(130, 2, IllegalAddress)
• Error reading _IO_EM_DI_03: Exception Response(130, 2, IllegalAddress)
• Error reading _IO_EM_DI_04: Exception Response(130, 2, IllegalAddress)
• Error reading _IO_EM_AO_00: Exception Response(131, 3, IllegalAddress)
• Error reading _IO_EM_AI_00: Exception Response(132, 4, IllegalAddress)

What's strange is that I can read the 4 DI if I read them as coils (0x01) NOT as discrete inputs (0x02).

This is my mapping. I've tried adjusting the registers but no luck.

modbus_mapping = {
    '_IO_EM_DO_01': {'address': 0, 'type': 'coil'},
    '_IO_EM_DO_02': {'address': 1, 'type': 'coil'},
    '_IO_EM_DO_03': {'address': 2, 'type': 'coil'},
    '_IO_EM_DO_04': {'address': 3, 'type': 'coil'},
    '_IO_EM_DI_01': {'address': 4, 'type': 'discrete_input'},
    '_IO_EM_DI_02': {'address': 5, 'type': 'discrete_input'},
    '_IO_EM_DI_03': {'address': 6, 'type': 'discrete_input'},
    '_IO_EM_DI_04': {'address': 7, 'type': 'discrete_input'},
    '_IO_EM_AO_00': {'address': 8, 'type': 'holding_register'},  # Assuming it's a single register
    '_IO_EM_AI_00': {'address': 24, 'type': 'input_register'},  # Assuming it's a single register
}

 

[Old Man]

Here are the most used Function Codes:

Most used Function Codes​

• Read:
• 01: Coils (FC=01)
• 02: Discrete Inputs (FC=02)
• 03: Multiple Holding Registers (FC=03)
• 04: Input Registers (FC=04)
• Write:
• 05: Single Coil (FC=05)
• 06: Single Holding Register (FC=06)
• 0F: Multiple Coils (FC=15)
• 10: Multiple Holding Registers (FC=16)

So if you wanted to address "_IO_EM_DI_01" you would map that to address 100001 since it's Discrete and then
you use Function 02 to read address 10001.

I suggest you study up on Modbus Addressing just Google it you will find plenty of information.

 

[bill1995]

Your advice helped me greatly. I was under the impression the IDE in CCW took care of that part of the addressing. My new table works as expected. I also was mistaken in how the addresses got mapped. I thought I needed "16" addresses for words but that part is managed by the address being "4xxxxx" or "3xxxxx" apparently. Thank you!