Logisim components behave very differently when trying to memorize an undefined value:
- the RAM component stores an "all ones" value (0b11...1),
- the Register component keeps the previous value,
- the Counter component resets to zero.
All Logisim components should share the same behavior. Ideally, this behavior should be configurable on a per-circuit basis. For educational purposes, one could therefore configure a circuit to memorize a conventional "error" value (e.g. 0xEE...E) when trying to load/store an undefined value.