Marilena Nardelli

Problem with  ADC on MC68HC908JL16

Discussion created by Marilena Nardelli on Oct 19, 2007
Latest reply on Oct 24, 2007 by Marilena Nardelli
Good morning!

To develope my project I'm using the emulator EML08JLJKE for the MCU MC68HC908JL16.
I have observed a wrong behavoir on two ADC channels (ADC12 and ADC9) specially when they work booth. On the signal is possible to see a spike, similar to capacitance's discharge, it is periodic, I think that the period is equal to the time used to come at the same instruction in the while for-ever loop.

I have setting the ADC module to work at bus frequency/8 (my bus frequency is 6MHz then the ADC clock frequency is 750KHz). I use single conversion mode, 10bit right justified with ADCSC write triggered mode enabled, long sample time configuration and obvious I have selected internal bus clock as the input source clock.
Every time I want read one channel, I set ADCSC register (ADCSC = channel_number) and when the flag COCO is set, I read the registers ADRH:ADRL.

I hope that the explanation is clear. Every suggestion is welcome, thanks.