Modbus emulation

Philip Gamblin

I have an industrial application. I need to monitor a limit switch for open. That's the easy part
The difficulty comes in communication. I need to have the stamp respond to a·Poll from the Master with a Modbus·variant· reply. I have the telemetry equipment, the master hardware and software. That is what we do here. What I am trying to accomplish is to create a simple, less expensive RTU (Remote Terminal Unit). I this case I only need to monitor 1 contact for open and then wait on the master to poll me so I can give it the contact status. The problem is I need to emulate Bristol Babcock's variant· of Modbus which is yet to be determined. The protocol is not
negotiable I have to be compatible with the other hundred or so units in·our installed base. Any ideas?

allanlane5

Yes, get a really really good description of "Bristol Babcock's variant of ModBus". I can't tell you how many times I've had to reverse engineer what was REALLY going on with a serial bus in order to add a new custom device.

Philip Gamblin

That should not be too difficult to accomplish. We use it all the time, it has just always been a "genie in a box " kind of thing. Like I drive my car all the time, but that doesn't mean I can rebuild a transmission.

Post Edited (Philip Gamblin) : 6/11/2005 11:28:26 PM GMT

allanlane5

Hmm, when was the last time YOU added a widget to your car computer, hmm? "not difficult to accomplish"? It can be a complete show-stopper, not to mention that the BS2 is single-tasking (no interrupts).

Philip Gamblin

The "not too difficult" part referred to getting the info on the protocol. Finding the information should not be "too difficult" implementation is, agreebly a much different matter. It is my hope that once interrogated, I'll use SEROUT to dump the appropriate bitstream in response.