> I coded things in assy and did not have problems but it was a user
> interface on a radar detector and again on a speedometer / tachometer
> system. when the A/D conversion was complete the code checked for a button
> press (voltage drop) then did comparisons based on voltage measurement
> with fairly wide tolerences (5 buttons, 8 bit conversion). The A/D ran in
> the background and the "state machine" ran the button routine when the A/D
> done flag was there from the main loop. Fast for a user interface does not
> need to be fast as far as processor capabilities are concerned. The
> processor ended running a 20 mhz crystal because of some more critical
> timing issues.
> Larry


I did this in a 15 button system. I used SIP resistor networks for the
voltage divider to get pretty good tempco matching. The pushbuttons just
selected off the divider and drove the A/D input. I used SPDT switches
"looping through" the unselected switches to avoid problems when multiple
buttons were down. This also gave a priority order to the switches.

The asm code was pretty simple. I put the ADC value in w, then added the
negative of a half step of the voltage divider. If the result was
negative, the input voltage was zero. I then successively added negative
"full steps" to w, checking for a negative result on each, and branching
to the appropriate code.

Harold

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