topic Re: MK24FN256VDC12 can enable internal pull-up register when open drain output in Kinetis Microcontrollers

MK24FN256VDC12 can enable internal pull-up register when open drain output

isaotakashima — Thu, 15 Feb 2018 08:11:30 GMT

I made the our evaluation board using the MK24FN256VDC12.

I want to reset external device using PTA1 with open drain output mode (PORTA_PCR1[ODE] = 1). I understand that require external pull-up resistor in this case, but our board does not have it.

Can I use internal pull-up resistor by PORTA_PCR1[PE] = 1 and PORTA_PCR1[PS] = 1 in open drain mode?

Anyway, I confirmed that I can use internal pull-up resistor with above settings (PE=1, PS=1) in open drain mode (ODE=1) using FRDM-K64F.

Please reply as soon as possible.

Best regards,

Takashima

Re: MK24FN256VDC12 can enable internal pull-up register when open drain output

jorge_a_vazquez — Thu, 22 Feb 2018 01:57:54 GMT

Hi Isao Takashima

Internal pull up is a weak resistor, so we normally recommend an external pullup, but this depends in the impedance needed for your application. If you already test this is a frdm board, then I don't see any problem, K24 and K64 are not different in GPIO module.

Hope this helps.
Have a great day,
TIC

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Re: MK24FN256VDC12 can enable internal pull-up register when open drain output

isaotakashima — Thu, 22 Feb 2018 09:34:16 GMT

Dear Jorge Antonio Alcala Vazquez,

Thank you for your reply.

We understand that Internal pull up is a weak resistor (according to data sheet it pull up is 20 - 50kohm), but we want to reduce BOM cost and board sapce.

We would like to make sure below description of PE bit of PORTx_PCRn register.

================================================================

Pull Enable
Pull configuration is valid in all digital pin muxing modes.
0 Internal pullup or pulldown resistor is not enabled on the corresponding pin.
1 Internal pullup or pulldown resistor is enabled on the corresponding pin, if the pin is configured as a digital input.

================================================================

For our understanding, this ”Pull Enable" function is effective only when pin is set to input.

Why can we use internal pull up even though we set the pin to Open Drain output (ODE=1)?

Is it because the pin is not driven when outputting HIGH?

Please teach us as soon as possible.

Best regards,

Takashima

Re: MK24FN256VDC12 can enable internal pull-up register when open drain output

jorge_a_vazquez — Thu, 22 Feb 2018 23:57:48 GMT

Hi Isao

For our understanding, this ”Pull Enable" function is effective only when pin is set to input.

Why can we use internal pull up even though we set the pin to Open Drain output (ODE=1)?

Sorry for this, Reference Manual gives an unclear description. You can actully use the internal pullup with Open Drain Output, there is no a problem here. Thanks for the comments

Hope this helps
Have a great day,
TIC