jbritt@hobbes.catt.ncsu.edu (Joe Britt) (11/29/90)
Help!
A friend of mine just got one of those 68HC11 evaluation boards from
Motorola. One project idea we had for it needs the A/D converter,
so we decided to try hooking up a potentiometer as a voltage divider
just for initial experimentation.
We connected VrefHI to +5v and VrefLO to ground. We connected one side
of the pot to +5, the other side to ground, and the center lug tothe A/D
input (Port E, bit 0). Then we wrote this simple little program to
grab bytes from the A/D converter and dump them out to the terminal
port.
We get stuff from the converter, but it looks screwy. Looking at the
pot's output with a voltmeter, we see a nice (LINEAR) swing from 0 to
5v. What we see on the terminal screen though, is usually one of 2
values: AA or 55. Sometimes it won't be so distinct, and it will
oscillate between several values.
The program is super-simple: once the a/d is set up, it waits (counts
down from $ff), grabs a sample, then counts down again.
What are we missing? Has anyone successfully used the a/d converter
on one of these boards?
muchos thanks in advance,
jbritt@eceugs.ncsu.edu
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