FA-89265 / Digital logic simulation / Member archive
Load ignored while count enable is low · case 05
A synchronous load issued with enable low does not change the counter.
Case contract
Input [m, q0, ops]: ops per clock [load, value, en, up]. Before the edge tc = en==1 and ((up==1 and q==m-1) or (up==0 and q==0)). At the edge load==1 sets q = value mod m (load has priority and ignores en); else en==1 counts up or down modulo m. Return [q after edge, tc] per clock.
Why this case matters
Counters are the most common sequential primitive; wrap, load priority and terminal-count gating are recurring simulation-model bugs.
One recorded failure
Sample boundary fixtureThis sample comes from the broken implementation of a controlled reproducer.
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| load with enable low | [[0, 0], [1, 0]] | [[3, 0], [4, 0]] | Failed |
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