SLC500 Messaging

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Dean Reimer

I want to send a message from a SLC 5/04 based on a one-shot change in the value of an integer word (I compare the value of the word with the value from the last scan). This change will happen on the order of once every several hours. I've had very little experience, and no training, in the use of the MSG instruction. If I trigger a message with a one-shot, do I need to latch it in with the EN bit? Should I use the one-shot to latch in a bit, then use this bit to execute the MSG instruction, maybe several times until a certain number of counts is made? Can I guarantee that the message is properly transmitted? How should I incorporate time-outs and the ER bit in my logic. This is the only MSG instruction that will reside in the processor, so I am not anticipating any problems overloading the buffer. My concern is that triggering the message only once leaves me vulnerable if there is an error. I've looked through the A-B manual on the instruction, but I don't really see an example of the best way to use this instruction. I'd appreciate any advice you could offer.
 
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Peter Nachtwey

An example of how to use the MSG block with DF1 is at http://www.deltacompsys.com/Files/rmcdf1.zip It shows how a SLC500 can control a motion controller that also looks like another SLC. In your application one rung should do it. NEQ OldData NewData XIO Msg.EN branch ; I forget the real name MSG Msg ; Msg control NXB ; next branch COPY NewData OlData Branch end ; I Forget the real name > I want to send a message from a SLC 5/04 based on a one-shot change in the value of an integer word (I compare the value of the word with the value from the last scan). This change will happen on the order of once every several hours. > > I've had very little experience, and no training, in the use of the MSG instruction. If I trigger a message with a one-shot, do I need to latch it in with the EN bit? Should I use the one-shot to latch in a bit, then use this bit to execute the MSG instruction, maybe several times until a certain number of counts is made? Can I guarantee that the message is properly transmitted? How should I incorporate time-outs and the ER bit in my logic. > > This is the only MSG instruction that will reside in the processor, so I am not anticipating any problems overloading the buffer. My concern is that triggering the message only once leaves me vulnerable if there is an error. I've looked through the A-B manual on the instruction, but I don't really see an example of the best way to use this instruction. > > I'd appreciate any advice you could offer. >
 
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