Determining Pulse Width with 18f84

aldinlapinig · Joined: 16 Dec 2005 Posts: 22

Hi everyone,

I want to determine the Pulse Width of a signal from a modulator to the PIC. Can anybody give me an idea on how I could do it with 18f84? Thank u so much...

kind regards,

-=alDin=- Smile

PICoHolic · Joined: 04 Jan 2005 Posts: 224

Do u mean 16F84 ?

Anyway, here's my suggestion:

Connect your signal to the external interrupt of the PIC (RB0).
1st configure the interrupt from Low to high
Once you get an interrupt, clear a timer and start counting and reconfigure your interrupt for high to low.
When you get a second interrupt, your pulse width will be held in your timer. Then reconfigure your interrupt to low to high... and so on...

Good Luck

Humberto · Posted: Fri Mar 17, 2006 11:30 am

aldinlapinig · Joined: 16 Dec 2005 Posts: 22

thanx for the immediate response man.. It'll help a lot. I wud like to ask u again. do u have any idea on how to generate the CRC-XMODEM checksum? I'm trying to interface an RFID reader module (TI product) with 18f877a. They'r using CRC-XMODEM algorithm (poly = 0x8408) for their data CRC. I tried to use CRC.C (of CCSC) but the pattern available for generating 16-bit CRC is only 0x1021 (CRC-CCITT). Any idea on how I cud modify the driver to fit my needs or write another driver? Any help will be highly appreciated. Thanx everyone!

-=alDin=-

Humberto · Posted: Sun Mar 19, 2006 9:42 am

This is a complete XMODEM CRC Protocol calculation posted by
J. Winpenny and for C2C compiler:

http://web.ukonline.co.uk/j.winpenny/pic/txrxmod.txt

Humberto