MCS-51单片机应用子程序：1.1.1 双字节无符号数加法

DADD: MOV R4,#00H MOV R5,#40H MOV R6,#60H MOV R7,#01H MOV 20H,R4 MOV 21H,R5 CLR C MOV A,R4 ADD A,20H MOV 20H,A MOV A,R5 ADDC A,21H JB D2,LOOP MOV R4,20H MOV R5,21H RET LOOP: MOV R4,#0FFH MOV R5, #0FFH RET