Where do I find slew rate data and which GPIO pins can it be changed on for a KL25Z128FM4?

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Where do I find slew rate data and which GPIO pins can it be changed on for a KL25Z128FM4?

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andrewhartnett
Contributor II

Trying to find rise and fall times for fast and slow slew rates on the GPIO pins, and also which GPIO pins on a KL25z128FM4 support slew rate configuration. I can't see it anywhere in the KL25 Family Ref manual, or in the KL25 Sub-Family data sheet.

Thanks

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Robin_Shen
NXP TechSupport
NXP TechSupport

The "Table 3-49. Ports Summary" of KL25P80M48SF0RM shows you can not control the Slew Rate. The default Slew Rate configuration are listed in that table, most of the common GPIO are default configured with Slow Slew Rate.

Table 3-49. Ports Summary.png
The Slow Slew Rate can be found in "Table 14. General switching specifications" of KL25P80M48SF0.

Table 14. General switching specifications.png
For other individually Fast Slew Rate you need to search "fall time" in KL25P80M48SF0. For example:

Table 31. SPI master mode timing on slew rate disabled pads.png

Best Regards,

Robin

 

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mjbcswitzerland
Specialist V

Hi Andrew

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Therefore no control possibility on the KL25.

Regards

Mark

uTasker developer and supporter (+5'000 hours experience on +60 Kinetis derivatives in +80 product developments)

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andrewhartnett
Contributor II

Thanks Mark - saw this table, but was confused by the next line "

And by bit 2 in the Portx_PCRn register:

And 11.2.1 which says

   Individual slew rate field supporting fast and slow slew rates on selected pins.

Seems very odd to include all that in the documentation if there is no ability to actually adjust the slew rate....

And also, really would like to know the minimum rise and fall times. 35ns for the maximum is fairly high. We're trying to diagnose an issue with electromagnetic noise on a board, and the rise and fall times can be a contributor. We were hoping to work it out through the documentation, but will measure it. And then if it is an issue, we were hopeful that we could adjust the slew rate to slow to correct it.

Regards, Andrew

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mjbcswitzerland
Specialist V

HI Andrew

There is a lot of cut-and-paste between user manuals (with some details not being relevant or not absolutely correct) so one needs to read between the lines a bit and do some cross checking. [The chip configuration details however often explain what needs to be overridden from the more standard text].

But, nothing replaces some practical testing to be absolutely sure....

Regards

Mark

uTasker - for more performance and faster, cheaper product development

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