The basic idea is to read the port periodically (called polling).

Your program will usually have a main loop that continues to execute
constantly.  Somewhere in the main loop, you need to test your port for
the desired input.
Here is some untested code:

portb  equ    0x06
mirrorb   equ   0x0C            ;; temporary register to store contents of
portB

;; Main Loop

MainLoop
        clrwdt          ;; do this once at the beginning of your main loop


        ;; Poll Port
        movf portb, w
        movwf mirrorb
        btfss   mirrorb, 1              ;; read, for example, pin 1 active
low on port B
        goto process
        goto someothertask

process
        <process input>

someothertask:

        < do some other tasks>

        goto MainLoop

If you can get this idea to work, that's great.  But for a real project,
this is too simple.  You should plan to get more sophisticated by
debouncing your input.  Read the input, if it is active, set a flag.  Read
the input later, and if it is still active, then execute the process
triggered by the input.  Start by getting your input to light an LED and
move up from there.

You will sometimes need to disable the input after it has been processed,
to prevent a key press from executing the process over and over.  In this
case, you ignore the flag until you have passed so many mainloops.  You
will need to tune this value to work with your application.

This is a very simple and straightforward approach.  I usually use timer
interrupts to process keypresses, but I would recommend you grapple
interrupts at a later time.

BTW, where are you located?

-- Lawrence Lile






Quah Yow Chun <asiact@TM.NET.MY>
Sent by: pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU>
10/09/02 11:48 PM
Please respond to pic microcontroller discussion list


        To:     PICLIST@MITVMA.MIT.EDU
        cc:
        Subject:        Reading Pulse Input


I am new to PIC, I am trying to write code to test whether an input
pulse exist. Any samples programs in machine language code to test exist
of input  pulse. I am using PIC16F84.

James

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