André ThomasAndré ThomasComputer Graphics Supervisor

EA Sports

LD BC,($4026) ; (20) fetch possible previous key value from ; CH_ADD LD ($4026),HL ; (16) put the fresh key value in CH_ADD.

LD A,B ; ( 4) fetch high byte. ADD A,$02 ; ( 7) test for $FF, no-key which will set ; carry.

SBC HL,BC ; (15) subtract the two raw keys. EX DE,HL ; ( 4) result, possibly zero, to DE.

LD HL,$4022 ; (10) now address system variable RESULT. LD A,(HL) ; ( 7) load A from RESULT_lo. OR D ; ( 4) check the OR E ; ( 4) subtraction result. RET Z ; ( 5,11) return if all three zero

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