單片機(jī)可預(yù)置可逆4位計(jì)數(shù)器

4．程序設(shè)計(jì)內(nèi)容

（1．兩個(gè)獨(dú)立式按鍵識(shí)別的處理過(guò)程；

（2．預(yù)置初值讀取的問(wèn)題

（3．LED輸出指示

5． 程序框圖

圖4.12.2

6． 匯編源程序

COUNT EQU 30H

ORG 00H

START: MOV A,P3

ANL A,#0FH

MOV COUNT,A

MOV P1,A

SK2: JB P3.6,SK1

LCALL DELY10MS

JB P3.6,SK1

INC COUNT

MOV A,COUNT

CJNE A,#16,NEXT

MOV A,P3

ANL A,#0FH

MOV COUNT,A

NEXT: MOV P1,A

WAIT: JNB P3.6,WAIT

LJMP SK2

SK1: JB P3.7,SK2

LCALL DELY10MS

JB P3.7,SK2

DEC COUNT

MOV A,COUNT

CJNE A,#0FFH,NEX

MOV A,P3

ANL A,#0FH

MOV COUNT,A

NEX: MOV P1,A

WAIT2: JNB P3.7,WAIT2

LJMP SK2

DELY10MS: MOV R6,#20

MOV R7,#248

D1: DJNZ R7,$

DJNZ R6,D1

RET

END