；以89c51单片机为例，假定用P1控制LED:

IO_LED EQU P1;

led_0 BIT P1.0;

led_1 BIT P1.1;

led_2 BIT P1.2;

led_3 BIT P1.3;

led_4 BIT P1.4;

led_5 BIT P1.5;

led_6 BIT P1.6;

led_7 BIT P1.7;

；定义开关LED的数据，假定LED正极一端接电源，另一端通过限流电阻接I/O端口：

DATA_CloseLED EQU 11111111B;

DATA_OpenLED EQU 00000000B;

ORG 0000H

AJMP MAIN

ORG 0030H

;-----------------------

；延时0.5秒程序（注：此延时函数摘自STC-ISP）

DELAY500MS: ;12.000MHz

PUSH 30H

PUSH 31H

PUSH 32H

MOV 30H,#4

MOV 31H,#205

MOV 32H,#180

NEXT:

DJNZ 32H,NEXT

DJNZ 31H,NEXT

DJNZ 30H,NEXT

POP 32H

POP 31H

POP 30H

RET

;-----------------------

；下面是主程序

MAIN:

MOV IO_LED,#DATA_CloseLED；同时关闭8个LED

LCALL DELAY500MS；延时0.5秒

MOV IO_LED,#DATA_OpenLED；同时打开8个LED

LCALL DELAY500MS；延时0.5秒

LJMP MAIN；循环

END;

上面程序演示了8个LED间隔0.5秒同时亮和灭的变化。