What is the COMP2_INM4 pin for in STM32F303C6 COMP module?

[Gahlen Feld]

Posted on June 28, 2017 at 14:06

The STM32F303C6 has COMP peripherals COMP2, COMP4 & COMP6.

Each of these comparators have a positive (INP) and negative (INM) input pin and an output (OUT) pin.

Furthermore the data sheet specifies for each comparator a pin named INM4.

I am wondering what these INM4 pins are for. Can somebody please tell me?

Thank you in advance,

Gahlen.

#stm32f303c6 #comp

[Gahlen Feld]

Posted on June 28, 2017 at 15:27

since all INM4 pins of the comparators are shared on the same pin PA4 there must be a correlation to DAC1OUT1, which cannot be used for the COMP input internally but only when assigning DAC1OUT1 to PA4 explicitly...

Can somebody confirm, that this is the only intention of INM4?

May be the reference manual in combination with the data sheet shall describe this in more detail...

[waclawek.jan]

Posted on June 28, 2017 at 18:24

Based on RM/DS reading, I'd say you still can use PA4 as negative input to one of the 3 comparators even if DAC1OUT1 is not enabled, as an input to external voltage.

jW

[Gahlen Feld]

Posted on June 30, 2017 at 08:35

thank you for the reply; you seem to be right, but in my case I have to use all of the 3 DACs as negative inputs for the 3 comparators (this is why I had chosen the STM32F303C6).

However, I in my opinion the documentation in RM/DS is lacking on this matter. It is still not clear why there is a further input named INM4. Is it only because it is on port A pin 4? Following that scheme the other negative inputs should have been named INM2 (COMP2),  INM2 (COMP4) & INM15 (COMP6).

In general the STM32's RM/DS is good and very specific. I am wondering that the description for the COMP inputs is unclear...

[Jan Waclawek]

Posted on June 30, 2017 at 09:09

It is still not clear why there is a further input named INM4. Is it only because it is on port A pin 4?

It's the 4th input on the negative-input-multiplexer, i.e. you set the multiplexer control register to 4 to direct that pin to the comparator input. There may be historical/backward compatibility reasons why the other physical pin(s) leading to comparator don't follow this naming scheme.

JW

[Gahlen Feld]

Posted on June 30, 2017 at 10:43

I am glad that you have a different view on the naming scheme of this pin.

This even emphasises that the descriptions in RM/DS are not precisely enough...

[Imen.D · Accepted solution]

Posted on July 03, 2017 at 09:37

Hello,

It’s a typo error. The index « 

y

 Â» in the COMPx_INM

y

is to be removed.

This is raised internally and will be updated in coming release of datasheet.

Thank you for contribution and bringing this to our attention.

Regards

Imen