topic LPC832: GPIO not working on default I2C and SWD pins in LPC Microcontrollers

LPC832: GPIO not working on default I2C and SWD pins

aaronm — Wed, 19 Apr 2023 21:28:12 GMT

Hi! I'm creating an X-Y matrix of LEDs and need a number of GPIO pins on an LPC832 (SOP20 package). However, pins 7,8 (SWD), and 9,10 (I2C) do not want to comply with the GPIO configuration. Pins 7 and 8 stay high, no matter how I set them, and pins 9 and 10 stay low. I looked at

https://community.nxp.com/t5/LPC-Microcontrollers/LPC802-SWD-disabling/m-p/1572427

But it didn't help. I've attached the compressed project so you can take a look for yourself. It could be that I overlooked something, but the other GPIO pins seem to work as expected.

Thanks for any insight.

Re: LPC832: GPIO not working on default I2C and SWD pins

aaronm — Fri, 21 Apr 2023 04:52:50 GMT

Ok, I understand the I2C pins - 9 & 10 - are open drain when in GPIO mode, so adding a pull-up resistor will allow the output to go high. I've tested that and it works.

I'm still stuck on pins 7 & 8 - the SWD pins. Do I have to disable SWD on chip startup?

Re: LPC832: GPIO not working on default I2C and SWD pins

Alice_Yang — Fri, 21 Apr 2023 05:24:27 GMT

Hello @aaronm

How about try to "After disabling the default SWD functions of pins, pull-down the P0_4 to the low state prior to resetting the MCU, after that, release the P0_4.".

Alice

Re: LPC832: GPIO not working on default I2C and SWD pins

aaronm — Fri, 21 Apr 2023 20:52:44 GMT

Got it. To disable SWD on the fixed pins, and enable GPIO on those pins, instead, I created this function and call it before BOARD_InitBootPins().

Note, however, after you do this, SWD will not work as expected until you enable ISP mode. To do that, connect pin 4 (PIO0_12) to ground, then touch pin 5 to ground and disconnect. SWD should work again.

// near the other #includes #include "fsl_swm.h" // somewhere in your source code void disableSWD () { CLOCK_EnableClock( kCLOCK_Swm ); SWM_SetFixedPinSelect( SWM0, kSWM_SWCLK, false ); SWM_SetFixedPinSelect( SWM0, kSWM_SWDIO, false ); CLOCK_DisableClock( kCLOCK_Swm ); }