modbus mask

[Arjennn]

Hello,

I have a question about MODBUS/TCP.

I have to write individual BITS to a holding register. Unfortunally, holding registers only accept unsigned values (numbers).

Therefore I need to convert my bit value (e.g. 101000 > 5).

But now I want to write a single bit value, without touching the other bit values. I think I need some kind of MASK for this to tell LabVIEW which individual bits I want to write.

Example in attachement.

Does anyone have any experience with a MASK in MODBUS/TCP in LabVIEW?

I have found on the internet things about "Holding Register Bit Mask Writes" and that Function Code 22 should be used, but I do not know how this can be used in LabVIEW.

Info about a mask in MODBUS (top of page 3)

http://www.micronor.com/products/files/AN112/AN112_NIModbusTutorial.pdf

How a mask should be used in writing a register (section 4.3.4 Mask write register (FC 22))

http://www.rtaautomation.com/modbustcp/

Thanks

Arjen

[Ranjeet_Singh · Accepted solution]

First read holding register then set your bit later write it. Its same only

[Arjennn]

Hello Ranjeet_Singh,

Thank you for your reply.

I have thought of that way of "fixing" it, but this solution will create extra (unnecesary) data traffic. It is not a nice solution.

There must be another way to do this ??

[ThiCop]

Hello Arjennn,

Do you have the hardware available.

Have you already tried to work with the NI Modbus Library and taken a look at the examples?

Do you have the hardware available so that you can do some tests?