兩字節(jié)壓縮BCD 碼轉(zhuǎn)換為兩字節(jié)二進(jìn)制數(shù)。算法如下：

BCD 碼abcd=1000a+100b+10c+d=10{10[10a+b]+c}+d，將各位BCD 碼分離出之后，即可根據(jù)此式轉(zhuǎn)換為二進(jìn)制

數(shù)。涉及到乘法運(yùn)算和多字節(jié)加法運(yùn)算。

0X20，0X21 中為BCD 碼，0X21 高4 位為最高位。轉(zhuǎn)換結(jié)果放在0X30，0X31 中。

main： MOV a，@0x79

MOV 0x20,a

MOV a,@0x54

MOV 0x21,a ;賦值

MOV a,0x20

and a,@0x0f

MOV 0x22,a

swapa 0x20

and a,@0x0f

MOV 0x23,a

MOV a,0x21

and a,@0x0f

MOV 0x24,a

swapa 0x21

and a,@0x0f

MOV 0x25,a ;BCD 碼展開(kāi)后存于0X22,0X23,0X24,0X25

MOV a,0x25, ;0X25 為最高位

MOV 0x30,a

MOV a,@0x0 ;多字節(jié)加法高位為0

MOV 0x31,a

MOV a,0x24

MOV 0x32,a

call a_b ;調(diào)子程

MOV a,0x23

MOV 0x32,a

call a_b

MOV a,0x22

MOV 0x32,a

call a_b

self: jmp self

a_b:

MOV a,@0x0 ;0X34,0X35 存儲(chǔ)中間結(jié)果

MOV 0x34,a

MOV 0x35,a

MOV a,@0x0a ;實(shí)現(xiàn)乘10

MOV 0x33,a

a1: MOV a,0x35 ;兩字節(jié)二進(jìn)制加法,在本例中高字節(jié)肯定無(wú)進(jìn)位

add a,0x31

MOV 0x35,a

MOV a,0x34

add a,0x30

MOV 0x34,a

jbc 0x03,0

inc 0x35

djz 0x33

jmp a1

MOV a,0x32

add 0x34,a

jbc 0x03,0

inc 0x35

MOV a,0x34

MOV 0x30,a

MOV a,0x35

MOV 0x31,a

ret

eop