Re: prosoft MVI56-GSC and control logix *HELP!*

Does anyone have experience with the prosoft cards with AB control

> logix? I'm working on a filling machine that uses 2 GSC's with a > Logix5555 controller that communicate with 2 banks of 12 flowmeters. > The manufacturer of the machine was unable to get the communications > between the flowmeters and GSC's to work properly and the problem has > been dumped in my lap. I have a controller and a pair of gsc's > sitting on my desk and I'm running prosofts sample program that just > echo's data recieved on the ports. I'm loosing up to 50% of the data > on the return. This is a similar problem that the machine originally > had. > If anyone has any experience writing RS232 flow control in logix, I > could use some advice.

Steve, I haven't used the Prosoft cards but have had a similar problem talking to RS232 devices using SLC's. It sounds to me like the port's input buffer is being cleared or over-written at the wrong times. I'm assuming you have an ASCII protocol and have the parity setting correct:

You mention "banks of 12 flowmeters.." does this mean you are using 232-485 converters? If so, you will need to make certain that your *hardware* handshaking is working properly before even trying to fault-find your software... but back to your problem:

Try coding the PLC to scan the entire input buffer (using a Read Input Byte-type command) for the end-of-message delimiter, counting the number of characters as you go. Assuming you are expecting a fixed-length response, when you get to the delimiter, if your count = the number of bytes you expect, (1) copy the entire input buffer to a PLC data string for processing and (2) clear the input buffer. If the count is *not* correct, clear/reset the buffer and wait for the next data packet.

With AB PLCs, it seems that each time you copy data from the input buffer you need to issue a buffer clear/reset command otherwise you will get junk the next time around. You can try using a Read Input Word-type command, but I've found in the past that if you get some data corruption and don't get the delimiter, you don't get any valid data either - just junk!

To test all this, use the lowest possible baud rate (like 300baud) and increase it only after you get things going again.

Good luck!

Cameron:-)

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Cameron Dorrough
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The flowmeters that I'm using (Bopp & Reuther) have their own communication cards that convert the signals from the flowmeters to rs232. I'm using separate comm ports on the Prosoft cards for each bank of 12, so the signal remains rs232. I did find a problem with the manufacturers program after monitoring the communications. The input image of the prosoft cards is 200 bytes and it uses 2 bytes to signal the amount of bytes are waiting to be processed. Same for the output table. The manufacturer had the LSB and MSB reversed so instead of sending 16 bytes, they were sending well over a hundred. They are writing to the first 16 on every cycle but there was some left over crap in the remaining buffer that wasn't getting cleared and causing some confusion to the flowmeters resulting in some really screwed up return messages. I'm going to make the changes and give it another try. Thanks for the help! Steve

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steveb

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