LPC MicrocontrollersのトピックUsing GPIO to pull a signal down

Using GPIO to pull a signal down

perdrix — Wed, 30 Aug 2023 17:02:09 GMT

I have a signal line that has a 3.3kOhm pull-up resistor to 3.3V.

I running code on an LPC2388 and trying to pull the line down to logic low using an FIO pin.

The IO pins I am using are configured thus:

The problem is that when I use FIOCLR to set the pins to logic zero, the actual voltage I measure is just under 1.4V (1.392V), which is definitely not logic low.

What am I doing wrong please?
Thanks, David

Re: Using GPIO to pull a signal down

xiangjun_rong — Thu, 31 Aug 2023 02:24:15 GMT

Hi,

For example, if you want to set/clear P0.2 pin and use the FIO to access, you can use the code:

SCS|=1<<0; //set SCS[GPIOM]=1 which can access the fast GPIO port FIO0DIR |= (1<<2); // P0.2 is output mode FIO0SET|=1<<2; FIO0CLR|=1<<2;

Pls have a try

XiangJun Rong

Re: Using GPIO to pull a signal down

perdrix — Thu, 31 Aug 2023 04:01:40 GMT

I had already set SCS |= 1; (NOT 1<<2 = that is the bit for the EMC).

I am already using FIO0CLR to attempt to pull the line down with the results I described.

Re: Using GPIO to pull a signal down

xiangjun_rong — Thu, 31 Aug 2023 04:59:05 GMT

Hi,

When the GPIO is configured as GPIO output mode, the GPIO pin is a push/pull pin, in other words, FIO0SET instruction will set the GPIO pin, FIO0CLR will clear the GPIO pin.

If the pin is in a middle voltage, I suppose that the pin is in input mode.

Pls try the following code and give me a result if the pin can be set or cleared.

XiangJun Rong

SCS|=1<<0; //set SCS[GPIOM]=1 which can access the fast GPIO port
FIO0DIR |= (1<<2);          // P0.2 is output mode
FIO0SET|=1<<2;
FIO0CLR|=1<<2;

Re: Using GPIO to pull a signal down

xiangjun_rong — Thu, 31 Aug 2023 08:11:14 GMT

Hi,

If you still fail to set/clear GPIO, pls post all the code so that we can have a review.

XiangJun Rong

Re: Using GPIO to pull a signal down

perdrix — Thu, 31 Aug 2023 09:07:01 GMT

Problem found - earth connection had come adrift! Sorry to take your time

Re: Using GPIO to pull a signal down

xiangjun_rong — Thu, 31 Aug 2023 09:18:57 GMT

Hi,

Glad to hear that you have found the cause.

XiangJun Rong