51单片机小实验——双字节二进制数的减法

减数首地址由30h给出，被减数和结果的存储单元首地址由31h给出。

jianshu data 30h

beijian data 31h

         org 0000h

         ljmp start

         org 0100h

start: mov r0,jianshu

         mov a,@r0

         mov r1,beijian

         clr c

         subb a,@r1

         mov @r1,a

         inc r0

         inc r1

         mov a,@r0

         subb a,@r1

         mov @r1,a

         jc exit

         inc r1

         mov @r1,#1h

exit:    sjmp $

                 end