Node-red wago 750-0881 modbus write

Node-RED
1

Hello,

I have a WAGO 750-0881 with 8 DI modules and 6 DO modules.

I would like to control the lighting managed by the 2nd DO module, channel 5.

When I use MODBUS WRITE, it asks for an address.

How can I find the address of this module and channel?

Thank you

2

Hello, I have a WAGO 750-0881 with 8 DI modules and 6 DO modules. I would like to control the lighting managed by the second DO module on channel 5. When I use MODBUS WRITE, it asks me for an address. How can I find the address of this module and this channel? Thank you

3

If your 750-881 is running a PLC program, the PLC runtime “takes control” of the I/O modules and you can’t write directly to the outputs. You will need to add separate Modbus variables to your PLC program and then use PLC logic to map those variables to the physical outputs. Internal memory for Modbus starts at Modbus Register 12288 which corresponds to Codesys memory %MW0.

If your 750-881 is not running a PLC program, then it does function as a Modbus Server. Physical outputs will start at Modbus Address 512, with all analog signals mapped first, followed by all digital signals.

For example, if you have two 8-channel digital output modules followed by a 2-channel analog output module, the two analog channels would be Modbus 512 and 513. All 16 DO would be Modbus 514. Channel 5 of the second DO module would therefore be Modbus register 514 bit 12 (counting from 0 as least significant).

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4

Thanks for answering

How do i know il my 750-0881 is running a PLC Program ?

Thanks

5

A program would only be running if you had used the WAGO-IO-Pro software (i.e. the old Codesys version 2.3) to create and download a program and stored it as a “boot project”.

When you power on the unit, does it DO anything? If so, there is likely a plc program running! If you aren’t sure, and don’t care if you wipe out an old program that might have been in place before you took over the project, you can use the Wago Ethernet Settings tool (available on the WAGO Download Center) to reset the unit back to factory defaults and erase any boot project that was there.

6

Or just try the Modbus Write from Node-Red and see if it works. If you can successfully turn a digital output on and off directly via Modbus, then you don’t have a PLC program running!

7

Hello,

Thanks for answering.

I’m using WAGO-I/O-CHECK, but when i click on CONTROL-MODE a popup displays “Impossible - PLC Programm is running”

Does it mean i cannot inject to an DO ?

Thanks

8

Correct. This means you have a plc program running and cannot take direct control of the I/O modules.

9

So, there is no way to control anything using nod-red ?

10

The important concept here is that you can’t control the I/O modules from two different sources at the same time. Since the running plc program has I/O control, you can’t directly operate the outputs via Modbus nor WAGO-I/O-Check. If you want to use Node-Red and therefore use the 750-881 strictly as a ModbusTCP remote-I/O device, you can do so but you need to turn off the program. There are several ways to do this, the simplest (and most temporary) is by setting the Run/Stop switch to the Stop (i.e. middle) position.