LPC1768 Output Open Drain With Pull-Up

[contr2889]

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

[Alice_Yang]

Hello contr2889,

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

BR

Alice

[contr2889]

@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

[frank_m]

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.

[contr2889]

@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.

[frank_m]

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.

[contr2889 · Accepted solution]

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.