Have you run https://github.com/Klaus2m5/6502_65C02_functional_tests https://github.com/Klaus2m5/6502_65C02_functional_tests ? See also https://www.righto.com

Have you run https://github.com/Klaus2m5/6502_65C02_functional_tests https://github.com/Klaus2m5/6502_65C02_functional_tests ? See also https://www.righto.com/2012/12/the-6502-overflow-flag-explained.html https://www.righto.com/2012/12/the-6502-overflow-flag-explai... I also note that you have the same code copy/pasted in every ALU operation which might be better expressed in one location for maintenance reasons.