Hi, the PIC24F family ref. manual for the ADC module doesn't really explain what Extended Sampling time is designed for or how long it is. Can anyone shed any light onto this? There's nothing descriptive in the PIC24FV32KA304 datasheet either, beyond the fact that it exists and can be enabled by setting EXTSAM

http://ww1.microchip.com/downloads/en/DeviceDoc/39739a.pdf

http://ww1.microchip.com/downloads/en/DeviceDoc/39995d.pdf

 

Hrmmm... an undefined delay for an indefinate ammount of time with no stated purpose. I went thru your documentation and the Microchip site and found no answers.

Mayhaps just leave it off and forget about it.

If you are still concerned make apost on Microchip's forums. If anyone knows they do.

 

Cool. Thanks for the confirmation ErnieM. Someone else has already asked Microchip and received radio silence.

http://www.microchip.com/forums/m974772.aspx

 

When automatic sampling is used, an extended sampling interval is extended between the time the sampling ends and the conversion starts.

51.7.3.3 SYNCHRONIZING A/D OPERATIONS TO INTERNAL OR EXTERNAL EVENTS The modes where an external event trigger pulse ends sampling and starts conversion may be used in combination with auto-sampling (ASAM = 1) to cause the A/D to synchronize the sample conversion events to the trigger pulse source. For example, in Figure 51-9, where SSRC<3:0> = 0010 and ASAM = 1, the A/D will always end sampling and start conversions synchronously with the timer compare trigger event. The A/D will have a sample conversion rate that corresponds to the timer comparison event rate

Sample time is the time that the A/D module’s S/H amplifier is connected to the analog input pin. The sample time may be started and ended automatically by the A/D Converter’s hardware or under direct program control. There is a minimum sample time to ensure that the S/H amplifier will give sufficient accuracy for the A/D conversion. The conversion trigger ends the sampling time and begins an A/D conversion or a repeating sequence. The conversion trigger sources can be taken from a variety of hardware sources or can be controlled directly in software. One of the conversion trigger options is an auto-conversion, which uses a counter and the A/D clock to set the time between auto-conversions. The Auto-Sample mode and auto-conversion trigger can be used together to provide continuous, automatic conversions without software intervention. When automatic sampling is used, an extended sampling interval is extended between the time the sampling ends and the conversion starts.

When you have auto-sampling and a external conversion trigger source the extended sampling interval is extra sampling time between triggers.

 

It's some undefined interval to allow something (not sure what?) to stabilize after a trigger event?

 

It's some undefined interval to allow something (not sure what?) to stabilize after a trigger event?

The extended sampling interval is determined by the timing of next trigger event from the previous trigger event. The ADC in this mode samples the input signal until the conversion trigger, after the conversion it goes automatically back into sample mode waiting for the next conversion trigger. This allows you to synchronize ADC timing using a asynchronous external/internal trigger in auto-mode.