Learn PIC Assembly Language Part - 8

Reading input from PORTS

This program teaches you to read the state of a port pin and makes the LED on if the switch is closed.

Here we use PORTA bit 1 to input the data, and PORTD bit 1 for flashing the LED. This programs reads the state of pin RA1 and flashes an LED on RD1, if the state is 1.
Program9.asm

list p = 18F452

#include < P18F452.INC >

org 00000 h

goto Start

org 0002A h

Start :

BSF TRISA,1,0 ; Setting bit1 of TRISA to make it as input

BCF TRISD,1,0 ; Clearing bit1 or TRISD to make it as output

Check :

BTFSS PORTA,1,0 ; Checking for RA1 ,whether its closed or open

goto Check

BSF PORTD,1,0 ; Making LED on RD1 – ON , when RA1 is set

Main :

goto Main ; Your program waits here

end

This program blinks an LED on RD1, when the switch on RA1 is pressed. I have given comment after the mnemonics for your clarity. If you have any doubts/clarifications, please contact me at my email address provided in the blog.

Wire up the circuit in a breadboard and press the switch on RA1 and check whether the LED is turning ON.