HW: Atmega32 clock 16mhz, ADC clock 125khz, ref 5V clean and steady, print conversions on GLCD
SW: interrupt driven adc , a ~100uS long 1000mV pulse is fed in to adc pin after each adc conversion is finished, witch means the pulse is present for the ~100uS time it takes the adc to make the conversion.
Problem: the conversion is ~600mV, the pulse seams to have about ~8 uS rise time, then it stabilize with an average of about 980mV.
I think that 8uS rise time coincides with the 1,5 clock cycle ( 12uS ) that avr takes for sample hold, and that gives the error in conversion.
I attached a snapshot of the scope with the pulse and measurements, the pulse is measured at the avr adc pin.
(GLDC prints conversions right, because i have other conversions printed witch are ok )
Any ideas might be helpful, on why or how to fix.