Digi BL1800 user manual Int vswitch

int vswitch;		// state of virtual		switch controlled by button
S1
main(){		// begin main program
		// set up parallel port A as output
	WrPortI(SPCR,NULL,0x84);
	WrPortI(PADR,&PADRShadow,0xff);		//	turn off all LEDs
	vswitch=0;		// initialize virtual switch off
(1)	while (1) {		//	Endless loop
	BigLoopTop();	// Begin a big endless loop
	// first task flash LED DS4 every second			for 200 milliseconds
(2)	costate {		//	begin a costatement
	BitWrPortI(PADR,&PADRShadow,0,3);		//	LED DS4 on
(3)	waitfor(DelayMs(200));		//	light on for 200 ms
	BitWrPortI(PADR,&PADRShadow,1,3);		//	LED DS4 off
	waitfor(DelayMs(800));		//	light off for 800 ms
(4)	}		//	end of costatement

//second task - debounce switch #1 and toggle virtual switch vswitch

//check button 1 and toggle vswitch on or off

costate {

(5)if(BitRdPortI(PBDR,2)) abort; // if button not down skip out

waitfor(DelayMs(50));	//	wait 50 ms
if(BitRdPortI(PBDR,2)) abort;	//	if button not still down skip
out
vswitch=!vswitch; // toggle virtual switch- button			was down 50
ms
while (1) {	// wait for button to be off 200 ms
waitfor(BitRdPortI(PBDR,2));	//	wait for button to	go up
waitfor(DelayMs(200));	//	wait for 200 milliseconds
if(BitRdPortI(PBDR,2)) break;//		if button up break
}	//	end of while(1)
}	//	end of costatement

//make LED agree with vswitch if vswitch has changed

(6)if( (PADRShadow & 1) == vswitch) { BitWrPortI(PADR,&PADRShadow,!vswitch,0);

	)
(7) }	// end of while loop, go back to start
}	// end of main, never come here

The numbers in the left margin are reference indicators and are not a part of the code. Load and run the program. Note that LED DS4 flashes once per second. Push button S1 several times and note how LED DS1 is toggled.

The flashing of LED DS4 is performed by the costatement starting at the line marked (2). Costatements need to be executed regularly, often at least every 25 ms. To accomplish this, the costatements are enclosed in a while loop. The term while loop is used as a handy way to describe a style of real-time programming in which most operations are done in one loop. The while loop starts at (1) and ends at (7). The function BigLoopTop() is

User’s Manual 49