topic Re: Vref interfering with GPIO PTB2 on KL03 in Kinetis Microcontrollers

Vref interfering with GPIO PTB2 on KL03

carlostadeoorte — Wed, 12 Aug 2015 16:50:18 GMT

Hello,

I would like to ask for your kind help with some problem involving Vref and GPIO.

I use the Vref voltage internally with a low-power buffer. At the same time, I use GPIO, in particular PTB2. However I see some interference on PTB2 presumably caused by Vref. To test my point, I did a sample program listed below.

I ran this program on my Freedom KL03. I removed R17 that connects PTB2 to the UART of the programming interface.

configure_gpio();

init_vref();

enable=0;

while(1) {

PTB -> PTOR|=0x1<<10; //LED

if(enable) {

PORT_HAL_SetMuxMode(PORTB_BASE_PTR, 2u,kPortMuxAsGpio);

GPIO_HAL_SetPinDir(GPIOB_BASE_PTR, 2U, kGpioDigitalOutput);

GPIOB->PCOR = 0x1 <<2u;

} else {

PORT_HAL_SetMuxMode(PORTB_BASE_PTR, 2u,kPortPinDisabled);

}

enable ^= 1u;

for(j=0;j<1;j++) { //delay

for (i=0;i<150000u;i++) { }

}

If I hook the oscilloscope to PTB2, I see an oscillation between 1.2V and 0.4V, which is not what I expect, I would have expected to see an oscillation between 1.2V and 0V. I also used breakpoints to test my point.

Have any of you experienced that problem? any suggestions?

Thank you!

Re: Vref interfering with GPIO PTB2 on KL03

jeremyzhou — Thu, 13 Aug 2015 02:25:38 GMT

Hi Carlos,

After had a brief look through the statement above, I think I already had an overview of your question.

However I still have some inquiries and want to confirmed with you.

1. After you remove the R17, you can hook the oscilloscope the PTB2 directly and without connect the the UART0_RX-TGTMCU, I think it will be more accuracy.

2. Does the interference still exist after you disable the VREF?

I'm looking forward to your reply.

Have a great day,

Ping

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Re: Vref interfering with GPIO PTB2 on KL03

carlostadeoorte — Thu, 13 Aug 2015 13:35:25 GMT

Hello Jeremy,

Yes, that what I did, I removed R16, R17 and I put the oscilloscope on the Arduino-like headers.

Thank you for looking into this!

-Carlos

Re: Vref interfering with GPIO PTB2 on KL03

jeremyzhou — Fri, 14 Aug 2015 01:31:27 GMT

Hi Carlos,

I was wondering if you can share the whole demo, then I can reproduce this phenomenon on my board.

I'm looking forward to your reply.
Have a great day,
Ping