Forced I/O in GE Series Five CPU IC655CPU500
- Status table – stores the states of the references
- Override table – has a bit for each Boolean reference that indicates whether or not the reference is overridden, Applies only to those reference types that supports overrides. Ladder logic cannot add or remove an override.
- Transition table – keeps track of Boolean references when they transition from 1 to 0 or 0 to 1. This information is used by one-shots and counters and is not accessible by the user.
- In the case of overrides, no coil type (output, latch, one-shot, timer or counter) can change the state of a reference that is overridden. However, data moves, table functions, math function and other similar functions (AKA mnemonic functions) can change the state of an overridden reference. This is because these functions deal with bytes and words and any Boolean reference assigned to the output of one of these functions is being treated as part of a larger block of data and overrides become irrelevant. To check for this type of scenario, you must perform an implicit search for the reference. An explicit search will not find a bit in the middle of a block of data in a mnemonic function.