Number of ADC channels in STM32F207Zx?

[optifier]

Posted on March 27, 2013 at 21:57

Hi,

Trying to get my head around how many ADC channels that are available in STM32F207Zx chip. Datasheet p14 Table3 claim ''Number of channels = 24''. Also on p.1 ''ADC with up to 24 channels''. OTOH, Reference manual p.204 says ''19 multiplexed channels allow it to measure signals from 16 external sources''. I can count to 24 pins on 144-pin chip that have ADC available. But none of the pins go beyond ADCxxx/IN15. Is this some sort of marketing trick to claim 24 channels in Datasheet? Or is there some multiplexing scheme that allow us to use 2 separate external sources connected to i.e. AD12/IN15 and ADC3/IN15 if we catch the result from first conversion before starting a second one with same INxx number? One of the major reasons we've looked into using STM32F207Zx chip was the large number of ADC channels advertised in Datasheet. Please enlighten me.. /Richard #adc-channels

[ezendam]

Posted on March 27, 2013 at 22:09

I am working with a stm32f4xx which has also 16 extexnal channels. But the adc can have up to 19 signals. 3 of them are internal signals like temp-sensor, vbat, etc. Can this be the case in your situation?

[optifier]

Posted on March 27, 2013 at 22:19

No, I'm aware of the 3 internal channels that make a total of 19 channels stated in Reference manual.

[raptorhal2]

Posted on March 27, 2013 at 22:51

Or is there some multiplexing scheme that allow us to use 2 separate external sources connected to i.e. AD12/IN15 and ADC3/IN15 if we catch the result from first conversion before starting a second one with same INxx number?

There are 3 ADCs, and some input channels can be connected to any one of 2 or 3 of these at a given time. The pinout definition defines which are which, e.g, ADC123_INx can be connected to one of the three, ADC12_INx to ADC1 or ADC2. Packages with a high pin count have an additional 8 channels connected to ADC3 only, and that provides for 24 external channels. Clear ? Cheers, Hal

[raptorhal2]

Posted on March 27, 2013 at 22:59

And if you are really channel hungry, the F3 series has 4 ADCs with something like 38 external channels.

Cheers, Hal

[optifier]

Posted on March 28, 2013 at 00:57

Hello Hal,

Well, clear is maybe not the correct word for my state of mind. If I understand correct you're saying:There ARE 24 ADC inputs on the chip and i.e. ADC12/IN15 and ADC3/IN15 can both be active at same time, not interfering with each other. That is, we can connect 2 separate sources and use ADC1(or ADC2) to read ADC12/IN15 and ADC3 to read ADC3/IN15 and expect two different results not related to / wiping out results of each other. And that Reference manual stating that 16 external sources can be connected are true for smaller pin-count devices, but not quite true for devices with ADC3. So far we'll be happy with 24 channels but good to know that there is a real monster out there with 38 channels. /Richard

[Tesla DeLorean]

Posted on March 28, 2013 at 01:42

That is, we can connect 2 separate sources and use ADC1(or ADC2) to read ADC12/IN15 and ADC3 to read ADC3/IN15 and expect two different results not related to / wiping out results of each other.

Indeed, the different ADCx units can scan through a different assortment of pins. You have to use DMA to store the results from each ADC conversion when dealing with multiple channels on a single unit.

[optifier]

Posted on March 28, 2013 at 09:48

Now I feel reassured.

Thanks to all that helped to set my mind at ease again.. /Richard