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FTM input capture on MKV58F1M0VLQ24

Question asked by Julian Schork on Dec 18, 2019
Latest reply on Dec 20, 2019 by Sabina Bruce

Hello all,

 

I am working with the MKV58F1M0VLQ24 Chip and I ran into confusion with the FTM input capture...

In general, I'd like to work with the FTM to measure the frequency of some fan tacho signals using the Kinetis SDK (Version 2.6.0). In detail, I wan't to measure those frequencyies using the FTM Counter Reset in Input Capture mode.

 

Currently I have four different tacho's attached to different FTM instances and channels. By now, it was possible to measure two of those signals using the FTM instances FTM1 and FTM2. As one of the fan tachos is connected to the FTM0 and another to the FTM3 instance, I noticed that those instances don't seem to work as an input capture module.

 

I noticed that for the instances FTM0 and FTM3, the IRST bit in the register CnSC was not settable as I did for the instances FTM1 and FTM2. Therefore the FTM counter for the channels in these instances is increasing, it's value is also written in the CnV register when my selected edge occurs but it is not reset in the same way it used to work with the FTM1&2 instances. As a result, my frequency measurement on those channels doesn't work this way.

 

After studying the reference manual multiple times, I'm still not really sure if the FTM instances FTM0 and FTM3 are just not usable for input capturing, or if I'm missing some configuration to make them do the work.

In the reference manual, I noticed the following cons:

- 44.1.1FTM Instantiation Information: only FTM1 and FTM2 have the feature of "general purpose"

- 44.1.7 Input capture options for FTM module instances: only FTM1 and FTM2 are mentioned for the external pin options

and pro:

- FTM CnV register value is changig, as if a selected edge triggers the storing of the current counter value to the CnV.

- 44.2.2 Features: "Each channel can be configured for input capture (...) mode"

 

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What I'm missing is a statement for the different instances, on what they can actually do and especially what they are not able to do...

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I would be glad to get some help and more information about this issue.

 

kind regards,

Julian

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