ADC Conversion time

bldcmotorcontro — Tue, 21 Feb 2012 19:03:27 GMT

Hi,

I have configured ANA0 and ANAB0 for simultenous conversion mode. I toggle a pin (make pin high

before START adc conversion command and make pin low in the AD1_OnEnd event) to get

the actual conversion time. But the time taken for one conversion with one sample is

10us.Conversion time selected in the processor expert panel is 1.594 µs.

In the datasheet it is said that it should take around 1.5us.

I am attaching the workspace for reference.

I am using 56f8037 (eval kit).

Regards

Arya

Re: ADC Conversion time

ProcessorExpert — Wed, 14 Mar 2012 00:35:24 GMT

Hi,

I have looked at your project an I have reproduced the behavior.

The reasons why you measured such time (I measured little bit less - something below 9uS, but it's similar) :

1. There is a big overhead of the interrupt itself. The interrupt disturbs the pipeline and saves and restores all registers

2. You are measuring first period after calling Start() method. The Start() method initilizes the adc and does some introductory setup.

3 Processor Expert component has also some additional overhead for handling verious checks for mode changes etc.

When I measured times afterwards, between on-end events, it was like 6.5uS.

The copnversion time of the ADC really is about 1.5uS but it's not possible to achieve such fast processing with interrupts.

best regards
Petr Hradsky
Processor Expert Support Team