How do I untangle who sets and clears each signal? - sample verification

FionaArcher0412 · 11 Aug 2026, 13:15 UTC

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FI
FionaArcher0412
I'm reviewing our non-safety job handshake for sample verification with Fairino FR5 in a PLC-coordinated fixture inspection cell, using an inspection coupon. The PLC sends a brief request, and our application sometimes misses it. I can't find anything clear about who owns each signal or when it gets cleared. Safety functions are independently engineered; this is the ordinary job interface

9 replies

NO
NoraChen1192
Replying to FionaArcher0412

Can you compare the request trace with your application's polls? Also note which side clears the request.

7 points
FI
FionaArcher0412
Replying to NoraChen1192

Our trace shows it rising and falling between two polls. The PLC clears it without an observed acknowledgement. No wonder the application misses it

16 points
NO
NoraChen1192
Replying to FionaArcher0412

@FionaArcher0412 Take an ownership table and a retained-request proposal to the interface owner. A request held until matching acknowledgement should settle the handshake in an offline review.

15 points
VI
VictorBaker0446
Replying to NoraChen1192

Settle it? Retaining a request fixes visibility, but can also keep an old request alive after a restart. Identity and reset rules matter.

8 points
NO
NoraChen1192
Replying to VictorBaker0446

Yes, I overstated that. Retention addresses the missed pulse. The offline review also needs matching identity, reset ownership and restart cases before the design is complete.

17 points
FI
FionaArcher0412
Replying to NoraChen1192

@NoraChen1192 Should I record readers as well as the single writer? Our existing phrase used by PLC doesn't distinguish setting, reading or clearing a field

11 points
NO
NoraChen1192
Replying to FionaArcher0412

Yes: writer, readers, meaning, set condition and clear condition. Then give each legal transition a concrete example.

17 points
FI
FionaArcher0412
Replying to NoraChen1192

The missed pulse is explained, and I've got an ownership review to work from. Our complete handshake behaviour is still open

2 points
NO
NoraChen1192
Replying to FionaArcher0412

The trace gives the review a concrete starting point. Keeping the overall handshake open is fair.

10 points

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