Modbus bit in word write

Is it possible to bit write into a word using latest version of Ignition by the way of Modbus I/P? It seems to read bits correctly however it does not wish to write them. The limited success I do have in writing seems to write a 1 into the word regardles of the bit position entered. Also the Server status page shows that the Modbus version is V2.2 when the Module labels the driver at V2.5
The running Ignition application is 7.5

I’ll assume you’re addressing the tag something like this, for example:


(Holding Register 1, bit 3)

Writing to the bit only works on Modbus devices that support it (Function Code 0x16, Mask Write Register). If your device doesn’t support it you should see an error in the console with a message to that effect. Or not, if you’re device’s Modbus implementation is poor. In that case your write request may just time out.

I’m not sure what screens your talking about re: the version numbers though. The server status page doesn’t show anything but the Ignition gateway version.

Thanks for the quick reply,

You may very well be correct in that the slave may not support function 16. I’m using an HMI (Lookout) as a test set, not the target PLC (Automation Direct) I’ll look into that.

The differing version numbers are located at:

Ignition–> Configuration --> Modules = ModbusV2 V2.5.0(b123)
Ignition–> Configuration --> OPC-UA --> Devices --> Add Device -->ModbusV2 = V2.2.0(b0)
Ignition–> Status --> Modules = ModbusV2 = V2.5.0(b123)
Ignition–> Status -->OPC-UA --> V2.2.0(b0)

And while I have you on the horn, the prefix of ‘C’ for coils is no longer allowed in the address configuration anymore? Is there a new list?

Many Thanks,

I’ll look into the version thing. It’s a cosmetic issue, not one causing any problems, so don’t worry about it.

Yeah, HR, IR, C, and DI aren’t allowed as prefixes in the address map any more. They never should have been since they interfere with the direct addressing scheme (creating SQLTags by hand with a direct address), which uses those prefixes. Unfortunately the restriction in the web UI only recently got put into place.