serial modbus read coils problem

[maxthedog]

Hi, I am using NImobdus llb to read and write coils, specifically "serial slave example.vi". I can only write or read 16 bits. has anyone seen this problem?

[Ebele_Obijiofor]

Hello,

Could you please provide some additional information about the problems you are having. I did find a forum post here, that sounds similar to what you've mentioned, and there's a fix provided.  Please see if this works for you. Thanks!

Regards,

[maxthedog]

I have seen the posts you mentioned, but I cannot see a fix from the post that makes sense to the vi's I have (lv modbus 8.2). the vi is not as simple as the one explained. If this was known by NI, why can't they fix it once so every person that stumble into this does not have to datamine the WEB to find a resolution.

I am writing 60 coils locally to the serial slave and reading them remotely from a plc. It works for the first 16 bits. we are building a simulator to benchtest plc programs.

thanks
Bernie

[jorgelopes]

Hi,

I have exactly the same problem.

I want to communicate more than 16 bits for coils (using the ModBus Ethernet Master for the Modbus Ethernet Slave ) and I can't.

Seems strange that this issue wasn't solved yet.

Can someone show me how to solve it?

Show the .vi or something...

[JB]

This is a known bug of the Modbus library. I agree that is it very annoying and surprising that this error wasn't corrected by NI in their official library !

Here the link to another thread from jorgelopes that will guide other users to a solution.

[jorgelopes]

This solution seems to be partial.

It solves the sending of data (coils) from the master to the slave.

But I'm still facing some issues regarding the discrete inputs.

Has anyone ever faced problems sending more than 32 discret registers from the slave to the master?

[jorgelopes]

The problem was solved by aplying the same solution to the MB Update Registers.vi