/* SW1=BUSY: When SW1=0 run. When SW1=1 quit */
/* SW2=ACK: When SW2=0 flash. When SW2=1 show the count */
	#include <stdio.h>
	#include <dos.h>
	#define datalpt1 0x3BC 	/* LPT1's I/O port address for D0-D7*/
	#define statlpt1 0x3BD 	/* status port address for LPT1 */
/* Notice: As shown in Chapter 18, in some PCs the port addresses of 378H,379H,and 37AH are assigned to LPT1. Modify 	the port addresses for your PC before you run it */
	main()
	{
	int i;
	while(inp(statlpt1) & 0x80) 	/* keep monitoring bit 7 for BUSY */
		{
		if(inp(statlpt1)&0x40) 		/* if ACK bit (bit 6) is high*/
			for(i=0; i <= 0xFF;i++) 	/* then count up*/ 
 	 			{
				outp(datalpt1,i);	/* and send it to LEDs*/
 				delay(200);		/*and wait in between */
				}
		else		/* otherwise flash since ACK bit 6 is low */
			{
			outp(datalpt1,0xFF);	/* Turn on all LEDs */
			delay(100);		/* Wait */
			outp(datalpt1,0x00); 	/* Now turn off all LEDs */
			delay(100);		/* wait. The flash rate is 100 ms */
			}
		}
	}

/* This example is adopted from a fine book "Technical C Programming" by Vincent Kassab, published by Prentice Hall */