Saturday, January 31, 2009

Input to the PIC 16f84


Now that we learned how to get output form the PIC ( flashing LED ) , we 'll learn to input the

Microcontroller by a push button . This will give you an idea to get order from the user to do an

action ( open door, turn-off lights, ......... ) .


; Button.ASM;******************************************************

list p=16f84


include "p16f84.inc"
org 0x00goto start

org 0x20

start


bcf INTCON,7

movlw 0x00

bsf STATUS,5


movwf TRISA

bcf STATUS,5

movlw 0xFF

bsf STATUS,5

movwf TRISB


bcf STATUS,5

againbtfss PORTB,0

call LED_ON


call LED_OFF


goto again

LED_ON

movlw 0xFF


movwf PORTA

goto again




LED_OFF

movlw 0x00


movwf PORTA

goto again

end
;***********************************************

The program makes the LED is ON when the Button is pressed , LED off when Button is released.

The only new command here is BTFSS which checks if the button is pressed or released.

What it makes is Bit Test F Skip if Set where F is a bit in register. This command is a

bit-oriented command. It means it deals with one bit of the register.

Build the following circuit in Proteus 7 ISIS :







Follow the steps you learned before to add the source code to the circuit and configure it , then

start simulation. Of course in this time you 'll add the Button.ASM source code.

Now , we 'll write the same program in C


//******************************************************



#include"pic.h"

main()

{

unsigned char i;



TRISA = 0 ; // Make PORTB output

TRISB = 0xFF ; // Make PORTB input

PORTA = 0 ; // Initialize PORTB

for(;;) // This is the infinite loop that keeps the PIC running

{


if ( PORTB == 0 )

PORTA = 1;

else

PORTA = 0 ;


}



}




//************************************************************

Note that the logic is inverted because the button by default inputs one to the PIC and when pressed inputs zero.

Again , you can configure the project for the C source code from this lesson.

You can download the project files and source code from here.

Enjoy.





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1 comment:

janpatfoort said...

thanx!

was very usefull