vertex troubleshooting questions dec. 4, 2001

1. Can the plc, loaded with "the" program, run by itself in an otherwise empty crate? Seems the answer should be yes. Why, after all, should it ever stop itself? Couldn't then claim to be robust.

Reasons it might stop:

issues a stop instruction (there is one) when disappointed in some way

OB31 is called automatically after an internal time out. The program then executes a STOP if the contents of accululator 2 are not equal to hex 1a21. The block comment is "stop after error" and the line commend is 'code "DB already existing" after call E DB......'

This is the only "STP" in the code.

stack overflow causes plc to stop ("S5 Programing II, page 21)

"scanning error" causes control to shift to OB28. If there is no OB28 (as in our case), the PLC

stops.

Similar stops if: addressing error from PII/PIQ; scan time exceeded; substitution error in FB call; input interrupt time out; data block transfer error; timed interrupt collision

commits a divide by zero or similar error that its operating system declares fatal, triggering an automatic shutdown