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Electronics => Microcontrollers => Topic started by: ipek.grgc on May 15, 2020, 01:47:38 pm

Title: STM32F1 PC13 LED
Post by: ipek.grgc on May 15, 2020, 01:47:38 pm

Hello everyone, hope you are doing okay.

In STM32F103C8's datasheet, Rev 17 page 33, it says:

" PC13, PC14 and PC15 are supplied through the power switch. Since the switch only sinks a limited amount of current (3 mA), the use of GPIOs PC13 to PC15 in output mode is limited: the speed should not exceed 2 MHz with a maximum load of 30 pF and these IOs must not be used as a current source (e.g. to drive an LED). "

But, as far as i know, in Blue Pill's design PC13 is driving a LED. How come? I am wondering.

Thanks! Be safe.

Title: Re: STM32F1 PC13 LED
Post by: exe on May 15, 2020, 01:57:14 pm

Nice catch. I guess this answers it: https://electronics.stackexchange.com/questions/440929/current-sinking-with-pc13-on-stm32f103c8t6 .
TL;DR: the current supposed to be within the limits if the board is done properly. But I can easily imagine that knock-off clone would violate this.

Title: Re: STM32F1 PC13 LED
Post by: Jeroen3 on May 15, 2020, 02:25:00 pm

Also, in the bluepill schematic PC13 is in sink configuration, not source. I suspect impact of sink is a lot smaller compared to source.

Title: Re: STM32F1 PC13 LED
Post by: exe on May 15, 2020, 08:13:43 pm

I think that text from the datasheet is inaccurate. Long below that I found this text:

> The GPIOs (general-purpose inputs/outputs) can sink or source up to ±8 mA, and sink or
source up to ±20 mA (with a relaxed VOL/VOH) except PC13, PC14 and PC15 which can
sink or source up to +/-3mA.

Page 65: https://www.st.com/resource/en/datasheet/stm32f103c8.pdf (https://www.st.com/resource/en/datasheet/stm32f103c8.pdf)