gnupic: 16f877 A/D problems
Subject:
16f877 A/D problems
From:
Declan Moriarty ####@####.####
Date:
14 Nov 2002 18:28:52 -0000
Message-Id: <02111418272000.01102@genius.chateau.dec>
Everything will work for me except the A/D on my little project
It simulates and assembles fine. When I clear ram and run the a/d, I get
0x01 and 0x9a in ADRESH & ADRESL. On the board, I either get 0x00 or 0xFF.
I am using one channel. Here's the voltages
Vdd 5V
-Vref ~1.5V
Now with respect to -vref
+Vref - 1.2V
AN0 ~ 0.25V
I have gone over the software and swapped pics until I'm blue in the face. I
took the steps from Microchip's 'f87 datasheet, page 113 in order. There is a
delay of seven seconds in step 3. This gave me 0x00 every time.
Then I tried the code from the midrange manual (example 23-5, on page 23-17)
This gives me 0xff. I tried on channel one with a pot. It doesn't make a
blind bit of difference what is out there - it just gives me 0xff or 0x00.
Can anyone point me at or provide a cast iron input stimulus file for this,
or code which works. I'm presuming the error is mine.
--
Regards,
Declan Moriarty
Applied Researches - Ireland's Foremost Electronic Hardware Genius
A Slightly Serious(TM) Company
Without the optimist, the pessimist wouldn't know how happy he isn't
