Tcp Modbus

[Bob Clarke]

Hi all, I'm hooking a PBW application up to a PLC.
Has anyone done Modbus communication over TCP?
All the threads I find are pretty old and done with serial com.

BobNorway

[Laurence Jackson]

Not Modbus, but if you're using A-B PLCs, I've got PB code for direct read and write of SLC500 data files via TCP. Let me know if interested.

[Bob Clarke]

Unitronics

Hi Laurence,
Sure I'm interested in anything that works, your code
will surely get me pointed in the right direction.
Haven't used AB for years they aren't that big here in europe.
I mainly use Siemens S7-300/400 but this particular
job is with a Unitronics V130.
Very powerfull and inexpensive units for smaller jobs.
BobNorway

[Laurence Jackson]

If you're using S7, I doubt whether my code will get you pointed in the right direction at all. It uses the proprietary A-B Client-Server Protocol (AB/Eth) which wraps up DF1 packets for transmission over TCP, so it's very vendor-specific. Outside of the protocol implementation, it uses the standard PB TCP statements which are documented in the help file. I suggest that you start at www.modbus.org - there seem to be a lot of resources listed there.

I used to program Siemens S5 - hated it! I had to program S7 once - hated it more - Give me Allen-Bradley any day - I'm afraid that I'd never even heard of Unitronics. PLC and HMI in one unit - hmm, interesting, I'll think I'll check that out some more.

[Marcel Kollenaar]

Don't know if it is still relevant yet? I've done something in Xbasic (Alpha Five). I believe it can be translated into Powerbasic.