Knowing nothing about your code, I'd suggest checking if the code uses the DAA instruction. It is by far the trickiest thing to get right. Don't assume well behaved code -- what happens if A=0x5C and B=0xF4 and you execute "add b; daa"? That is, if you attempt to correct a sum which didn't start with valid decimal digits.
stevekemp|2 days ago
(The z80 emulation was the only thing I didn't write myself, though it does pass the standard test-programs I've not looked at how complex/complete their testing is.)