Is there Transition Time when switching between analog inputs?

[yundm]

Posted on August 02, 2006 at 13:47

Is there Transition Time when switching between analog inputs?

[yundm]

Posted on August 01, 2006 at 16:15

I'm selecting ST72F321 for my application -- testing ADC of 16 channels one by one as soon as possible.

I only find the 7.5us of ''Conversion Time'' of ADC in manual. I can't find the ''Transition Time'' when switching from one analog input to another. A electrical characteristic of ''Transition Time'' can always be found in corresponding databook if I use special Analog Multiplexer IC. How do I consider ''Transition Time'' in ST7? Supposing I switch ADC from AIN0 0f 0V to AIN1 of 4V: Does the voltage of 4V appear in ADC input immediately without any distortion or delay? How quickly? How many time? us or ns? Is ADC result always 4V after 7.5us if I start ADC immediately even when there is distortion in ADC input in the beginning?

[pjr]

Posted on August 02, 2006 at 13:47

Section 5.6.2 of the ST7 8-Bit MCU Family User Guide states any write to ADCCSR stops the conversion in progress and starts a new one. My guess is this would cover any delay needed.

Try it. Set up several ( or all ) AIN pins with known analog values. Test code could select one input ( which should re-start a conversion on that AIN input ). When the EOC bit is set, store the result and pick the next AIN input. Do this for all the AIN inputs you setup. Do the first conversion measured values compare favorably with the input values you supplied? pjr