AndersNielsen on Wed 23 Mar 2022 wrote:
If they’re not from a reputable source I would test with a BRA instruction if they’re supposed to be cmos.
I had that exact issue last week so maybe I’m just seeing it everywhere.
Dodgy NMOS components may become more widespread due to the chip shortage. A chip may say 65C02 but unconditional branch is a definitive test.
adrianhudson's suggestion makes me consider dodgy power in the first moments of operation. If processor comes out of reset before power is stable then dodgy writes may occur before the system becomes reliable. One symptom may be missing bits from the first subroutine return address but otherwise faithful operation.
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