BasicMicro - Forums

Hi All, my first post I think but I read this forum regularly.
My query regards an anomaly I've noticed with the Atom 28 A/D. I've been using the Atom 28 for several years now in an application I developed, all with no problems.
Basically my app uses 3 10k pots (fed from the 5v supply from the Atom) to analogue inputs. I use pins 16,17 and 19 - the old ax0, ax1 and ax3 (why I didn't logically use ax2 I don't know, but I did ). My design left pin 18 floating. When I received my first Atom 28 RevD I found that pin 19 (ax3) gave a constant reading regardless of the pot setting even though I could measure the voltage changes directly on the pin.
Deciding that maybe pin 19 had a problem my first response was to bridge pin 19 to pin 18 (ax2) so that I could use it instead. To my surprise when I retried my programme (without modification) pin 19 was now working ok. This wasn't a one off - every Rev D chip from then on had the same issue, my PCB design now has that bridge between pin 18 and 19 regardless.
I haven't pursued this finding to any great dregree, I don't have the time to experiment and I just wanted something that worked.
Has anybody noticed this before? If so please point me to the posts. If not maybe BM could look into it.

Regards Richard

Hello Richard. That's.... wierd. It sounds like the programmer bobbled his pins mapping and assigned AX3 and AX2 incorrectly, maybe even swapping them. You could change the AX# designator to the P# and point to the pin directly. I don't know how large or convoluted your code is, but couldn't you use the editor to find and reassign the pins?

I just checked the data sheets. Only the 24 and 40 pin module have AX# pins. I don't remember ever seeing AX-anything on 28 pin modules, but I didn't own one until BMicro gave me a couple to troubleshoot problems on the forums. Please confirm which part you have, ie, number of pins and is it a module or DIP part?

Later!

_________________
kenjj
http://blog.basicmicro.com/
http://kjennejohn.wordpress.com/

Hi ken, how are you?

My mistake (read the data sheet properly Richard).
Your "bobbled" comment lit a little light in my dim brain.
On the previous versions of the Atom 28 the A/D designators were ax0, 1, 2 and 3. The advent of the Rev D chip saw these designators dropped (presumably because it now offered more A/D capability) - and yes two of the assignments were "swapped".
The changes were:
ax0 to p16 (A/D ch0)
ax1 to p17 (A/D ch1)
ax2 to p19 (A/D ch3)
ax3 to p18 (A/D ch2)

As you can see, the last two are reversed from the previous design - hence my error.

Cheers Richard