topic Re: LPC1768 Output Open Drain With Pull-Up in LPC Microcontrollers

LPC1768 Output Open Drain With Pull-Up

contr2889 — Mon, 28 Mar 2022 23:04:17 GMT

Hi Everyone,

I am stuck trying to set a pair of pins in Open Drain mode with internal pull ups, I am using LPC1768 board. How I can do that? also, How I can know the value of this internal pull up resistor? Thanks for your help.

Best Regards

Re: LPC1768 Output Open Drain With Pull-Up

frank_m — Tue, 29 Mar 2022 08:06:57 GMT

Skimming over the sections in the MCU user manual, I see no generic configuration for internal pull-up/pull-down resistors for GPIOs. I have seen this on other MCUs, and other vendors, though.

The only OD pins are those associated with I2C, and here you need external pull-up´resistors.

It has been tried with other MCU's, but I2C does not work with internal pull-ups, which are usually in the 40..50 kOhm range.

Re: LPC1768 Output Open Drain With Pull-Up

contr2889 — Tue, 29 Mar 2022 13:47:13 GMT

@frank_m I thought to have pins with OD and pull-ups would be possible but if is not, then my only option is to use external pull-ups. Thanks for your reply.

Re: LPC1768 Output Open Drain With Pull-Up

frank_m — Wed, 30 Mar 2022 05:45:49 GMT

The LPC17xx is a more "seasoned" model, and AFAIK designed to be pin compatible with LPC23xx devices.

I have checked the pinout and the GPIO section of the MCU user manual, and found no hint about configurable pull-up/pull-downs. To name some examples, the LPC546xx has this option (in the IOCON register), as most STM32s have.

Re: LPC1768 Output Open Drain With Pull-Up

Alice_Yang — Wed, 30 Mar 2022 07:04:28 GMT

Hello contr2889,

How about PINMODE register, you can check UM for detail:

Alice

Re: LPC1768 Output Open Drain With Pull-Up

contr2889 — Wed, 30 Mar 2022 17:26:39 GMT

Hi @frank_m , thanks for your help. I was also looking on the manual for a solution and I found something I can use as you can see in the attached image.

I will try it but still I need to know the value of these pull ups resistors.

Re: LPC1768 Output Open Drain With Pull-Up

contr2889 — Wed, 30 Mar 2022 17:28:20 GMT

@Alice_Yang thanks for your reply. I am trying this now but still I need to know the value of these pull ups resistors.

Regards