8051 micro controller programming

An Application software requires an accurate 0.25 second delay function
to flash an LED. Show how you would program the C8051F020 to
generate such a delay using interrupts.

A student needs to do his homework. Show us some effort.

kk.... sory .. i have done it with timer 2 ... bt i dont know how to specify the time delay... :-)

prog:

Code:

//-- Filename : Lab3A.c
//-- This program makes the 4 green LEDs (on P5.4 to P5.7) blink (all together)
//-- Uses Timer 2 and interrupts to control the blinking (on/off) period.
//-- (Using Timer 4 is very similar to Timer 2)
//-- Uses 2 MHz internal Oscillator (default)

#include <c8051f020.h>			  // SFR declarations

//------------------------------------------------------------------------------------
// 16-bit SFR Definitions for 'F02x
//------------------------------------------------------------------------------------

sfr16 DP     = 0x82;            // data pointer
sfr16 TMR3RL = 0x92;            // Timer3 reload value
sfr16 TMR3   = 0x94;            // Timer3 counter
sfr16 ADC0   = 0xBE;            // ADC0 data
sfr16 ADC0GT = 0xC4;            // ADC0 greater than window
sfr16 ADC0LT = 0xC6;            // ADC0 less than window
sfr16 RCAP2  = 0xCA;            // Timer2 capture/reload
sfr16 T2     = 0xCC;            // Timer2
sfr16 RCAP4  = 0xE4;            // Timer4 capture/reload
sfr16 T4     = 0xF4;            // Timer4
sfr16 DAC0   = 0xD2;            // DAC0 data
sfr16 DAC1   = 0xD5;            // DAC1 data

enum {NORMAL, HIGH};
unsigned char count;

//------------------------------------------------------------------------------------
// Function PROTOTYPES
//------------------------------------------------------------------------------------
void init_Port(void);         		// general system initialization
void Init_Timer2(unsigned int counts);
void Timer2_ISR(void);		//-- ISR for Timer 2

void main(void)
{
	unsigned char blink_speed = NORMAL;
	count = 0;

	EA = 0;		//-- disable global interrupts
				//-- It is a good idea to disable interrupts before all the initialisation
				//-- is complete

	//-- disable watchdog timer
	WDTCN = 0xDE;
	WDTCN = 0xAD;

	init_Port();

	if (blink_speed == NORMAL)
		Init_Timer2(7203);	//-- Initialise Timer2 to generate interrupts every 350ms
	else	//-- blink_speed is HIGH
		Init_Timer2(53036);	//-- Initialise Timer2 to generate interrupts every 75ms

	P5 = P5 & 0xFF;			//-- turn ON the four LEDs

	EA = 1;		//-- enable global interrupts

	while (1);	//-- go on forever (endless loop)

}

void init_Port(void)
{
	//----- Configure the XBRn Registers
	XBR0 = 0x00;
	XBR1 = 0x00;
	XBR2 = 0x40;					  // Enable the crossbar, weak pullups enabled
	// To disable weak pull-ups, XBR2 = 0xC0;

	//------ Port configuration (0 = Open Drain Output, 1 = Push Pull Output)
	P0MDOUT = 0x00;				  // Output configuration for P0 
	P1MDOUT = 0x00;				  // Output configuration for P1
	P2MDOUT = 0x00;				  // Output configuration for P2 
	P3MDOUT = 0x00;				  // Output configuration for P3 

	//-- Port 7-4 I/O Lines
	P74OUT = 0x08;				  // Output configuration for P4-7
								  // (P5[7:4] Push Pull) - 4 LEDs
								  // (P5[3:0] Open Drain) - 4 Push-Button Switches (input)
								  // (P4 Open Drain) - 8 DIP Switches (input)

	//-- Write a logic 1 to those pins which are to be used for input
	P5 |= 0x0F;
	P4 = 0xFF;
}

//-- Configure Timer2 to auto-reload and generate an interrupt at interval
//-- specified by <counts> using SYSCLK/12 as its time base.
void Init_Timer2 (unsigned int counts)
{
	CKCON = 0x00;		//-- Define clock (T2M). Timer 2 uses system clock DIV BY 12
//	CKCON |= 0x20;		//-- if you want to use system clock
	T2CON = 0x00;		//-- T2CON.1 = 0 -->T2 set for Timer function (C/T2) i.e.
						//--				incremented by clock defined by T2M
						//-- T2CON.0 = 0 -->Allow Auto-reload on Timer2 overflow (CP/RL2)
						//-- T2CON.3 = 0 -->High-to-Low transitions on T2EX ignored (EXEN2)
						//-- T2CON.2 = 0 -->Disable Timer2

	RCAP2 = counts;	//-- Init reload values in the Capture registers
	T2 = 0xFFFF;		//-- count register set to reload immediately when the first clock occurs
	IE |= 0x20;			//-- IE.5, Enable Timer 2 interrupts (ET2)
	T2CON |= 0x04;		//-- start Timer2 by setting TR2 (T2CON.2) to 1
}

//-- Interrupt Service Routine
//-- This routine changes the state of the LEDs whenever Timer2 overflows.
void Timer2_ISR (void) interrupt 5
{
	T2CON &= ~(0x80);		//-- clear TF2. This is not automatically cleared, must be
							//-- done by software upon overflow.

	P5 = P5 ^ 0xF0;			//-- toggle the four LEDs using EX-OR with '1'
}

The code you posted says:

Code:

if (blink_speed == NORMAL)
		Init_Timer2(7203);	//-- Initialise Timer2 to generate interrupts every 350ms
	else	//-- blink_speed is HIGH
		Init_Timer2(53036);	//-- Initialise Timer2 to generate interrupts every 75ms

That could lead to something interesting. (ETA: Granted I have no idea how 7203 and 53036 relate to 350 and 75, but hopefully you do.)

Wow. In 9 minutes you went from knowing nothing to coming up with that "fully working" program? I think you're too smart for all of us and you don't need our help. Wait...

That code has nothing to do with your assignment. It blinks LEDs every 75 or 350 milliseconds. Nothing to do with precise .25 second delay. Actually, it looks like your code might have come from section 8.11 of this e-book: Embedded Programming or maybe from here: http://www.people.vcu.edu/~jhtucker/...ghter Card.pdf.