;等周期脈寬調(diào)制PWM
;晶振：12MHz
;89C51

P_PWM1 EQU P1.0
cycle EQU 1000 ;PWM的周期（單位微秒），則頻率為1000赫茲

cycle_high EQU 500 ;一個(gè)周期內(nèi)，PWM端口為高電平的時(shí)間(初始值）

DSEG AT 20H

ORG 40H

PWM_HIGH_L DATA 40H
PWM_HIGH_H DATA 41H ;PWM端口為高電平時(shí)，定時(shí)器寄存器的值

PWM_LOW_L DATA 42H
PWM_LOW_H DATA 43H ;PWM端口為高電平時(shí)，定時(shí)器寄存器的值

ORG 60H ; stack origin
stack: DS 20H ; stack depth

CSEG

ORG 0000H ; power on/reset vector
jmp on_reset

ORG 0003H ; external interrupt 0 vector
reti ; undefined

ORG 000BH ; timer 0 overflow vector
reti ; undefined

ORG 0013H ; external interrupt 1 vector
reti ; undefined

ORG 001BH ; timer 1 overflow vector
JMP TIMER1_ISR

ORG 0023H ; serial I/O interrupt vector
reti ; undefined

;***********************************************************************************
;系統(tǒng)初始化等
ORG 0033H ; begin code sPACe
USING 0 ; register bank zero
on_reset:
MOV R7,#00H
DJNZ R7,$ ;延時(shí)
mov sp, #(stack-1) ; initialize stack pointer

;禁止各中斷
MOV IE,#00H
MOV IP,#00H
SYS_INIT:
MOV R0,#00H
SYS_INIT_LOOP:
MOV R1,#00H
DJNZ R1,$
DJNZ R0,SYS_INIT_LOOP ;延時(shí)0.13S

;內(nèi)部RAM(30H-5fH)清零
MOV R1,#30H
MOV A,#0
ZERO_LOOP: MOV @R1,A
INC R1
CJNE R1,#60H,ZERO_LOOP

;定時(shí)器1初始化
MOV TMOD,#00010000B ;方式1，16位定時(shí)器模式

MOV PWM_HIGH_L,#LOW(65536 - cycle_high)
MOV PWM_HIGH_H,#HIGH(65536 - cycle_high)

MOV PWM_LOW_L,#LOW(65536 - (cycle - cycle_high))
MOV PWM_LOW_H,#HIGH(65536 - (cycle - cycle_high))

SETB P_PWM1 ;先輸出高
MOV TL1,PWM_HIGH_L
MOV TH1,PWM_HIGH_H

SETB ET1 ;T1開中斷
SETB EA ;開總中斷
SETB TR1 ;開定時(shí)器1

MAIN_LOOP:
;主循環(huán)
SJMP $

;********************