topic Re: LPC1768 Open Drain Output settings in LPC Microcontrollers

LPC1768 Open Drain Output settings

contr2889 — Thu, 31 Mar 2022 19:14:47 GMT

Hi everyone,

I am trying to use lpc1768 to have 2 pins with Open Drain output (p2.2 and p2.2) and external pull ups. When I set these pins only as output I get pulses with correct timing but when I add this line "LPC_PINCON->PINMODE_OD2 |= ((1<<1)|(1<<2))" I get a weird behavior in these pins, not matching the timing and getting extra pulses.

My code is the next:

void Sensor::init() { LPC_PINCON->PINMODE_OD2 |= ((1<<1)|(1<<2)); LPC_GPIO2->FIODIR |= ((1<<1)|(1<<2)); LPC_GPIO2->FIOCLR |= ((1<<1)|(1<<2)); } void Sensor::measure(void) { LPC_GPIO2->FIOSET |= ((1<<1)|(1<<2)); wait_us(50); LPC_GPIO2->FIOCLR |= ((1<<1)|(1<<2)); wait_us(50); LPC_GPIO2->FIOSET |= ((1<<1)|(1<<2)); wait_us(50); LPC_GPIO2->FIOCLR |= ((1<<1)|(1<<2)); }

What I am doing wrong to get OpenDrain output with the correct timing?

Thanks for your help, Regards.

Re: LPC1768 Open Drain Output settings

DanielRuvalcaba — Fri, 01 Apr 2022 22:34:56 GMT

Hello,

I noticed that with that line of code you just mentioned, you are writing a 110’b in the PINMODE_OD2 register and I believe that is incorrect, because that register can only be 1 or 0. In this case, the register stays with a value of 0, and that is configuring the register in not open drain mode. Could you please try to change that value to 1?

Regards, Daniel.

Re: LPC1768 Open Drain Output settings

contr2889 — Mon, 04 Apr 2022 04:20:32 GMT

@DanielRuvalcaba Thanks for your reply.

I follow your advice and I changed my code to clearly set the bits in 1'b but I still have the same problem. Here you can see the test code that I implemented:

void Sensor::init() { Log::info("PINSEL4: %X", LPC_PINCON->PINSEL4); Log::info("LPC_GPIO2->FIODIR: %X", LPC_GPIO2->FIODIR); Log::info("PINMODE4: %X", LPC_PINCON->PINMODE4); Log::info("PINMODE_OD2: %X", LPC_PINCON->PINMODE_OD2); LPC_PINCON->PINSEL4 &= 0xFFFFFFC3; LPC_GPIO2->FIODIR |= 0x00000006; LPC_PINCON->PINMODE4 |= 0x00000028; LPC_PINCON->PINMODE4 &= 0xFFFFFFEB; LPC_PINCON->PINMODE_OD2 |= 0x00000006; Log::info("PINSEL4: %X", LPC_PINCON->PINSEL4); Log::info("LPC_GPIO2->FIODIR: %X", LPC_GPIO2->FIODIR); Log::info("PINMODE4: %X", LPC_PINCON->PINMODE4); Log::info("PINMODE_OD2: %X", LPC_PINCON->PINMODE_OD2); } void Sensor::measure(void) { LPC_GPIO2->FIOSET |= 0x00000006; wait_us(50); LPC_GPIO2->FIOCLR |= 0x00000006; wait_us(50); LPC_GPIO2->FIOSET |= 0x00000006; wait_us(50); LPC_GPIO2->FIOCLR |= 0x00000006; wait_us(50); }

And this is what I get in the logs:

PINSEL4: 0
LPC_GPIO2->FIODIR: 1A0
PINMODE4: 28BFC
PINMODE_OD2: 0
PINSEL4: 0
LPC_GPIO2->FIODIR: 1A6
PINMODE4: 28BE8
PINMODE_OD2: 6

Then I can see that every bit is set correctly but still I got no pulses on the pins p2.1 and p2.2. Every test was made with a 10k resistor to 3.3V for pullups, but nothing happens. But if in the method measure() I put a longer delay as wait_us(1000), I get two pulses but with an incorrect random width.

As I said before, If I set these pins as simpe outputs without opendrain, then I get two pulses with the correct width of 50us and separation of 50us.

Which could be the problem here?

Re: LPC1768 Open Drain Output settings

contr2889 — Tue, 05 Apr 2022 21:29:19 GMT

The solution for me was not use pins p2.1 and p2.2, instead I changed them for p0.24 and p0.25 to have two pins in open drain mode.