How do I change polarity of the SPI data pin on the FRDM K64F

Questions » How do I change polarity of the SPI data pin on the FRDM K64F

9 years, 8 months ago.

I'm using the SPI interface on PTD1-PTD3 and the I/O pin polarity is inverted, e.g. logic high between output words. How do I change the default polarity to be logic low?

Thanks!

Michael

3 Answers

9 years, 8 months ago.

I believe that is the default on the Freescale ones, high output when not used. The clock polarity/phase can be changed to comply with the required SPI waveforms, but I don't think the SPI data polarity is ever defined. I believe for example the NXP microcontrollers put the data pin in high-Z mode when they aren't used.

If it is important for you, you can manually switch it to a GPIO input node, or low GPIO output. (I have had for example a situation where the SPI device could be disabled by turning of the power supply, but due to the high data pin on Freescale devices it was still semi-powered via ESD diodes).

Accepted Answer

I used mode 3, it seems that the MOSI jumps up too early and makes the LSB always be "1". Please refer to the picture I attached below.

posted by Zhe Zhang 11 Mar 2015

Zhe Zhang

9 years, 1 month ago.

/media/uploads/zhyena/frdm_k64f_spi_mode3.png

FRDM_K64F, SPI MODE 3 Supposed to send 170 ( 0xAA), but received 171. It seems that the MOSI jumps up too early and makes the LSB always be "1". How can I solve the problem?

FRDM_K64F, SPI MODE 3 Test

#include "mbed.h"
 
SPI device(PTD6,NC,PTD5);

int main() {
    int i = 0;
    device.format(8,3);
    while(1) {
        device.write(0x55);
        device.write(0xAA);
        wait(1);
    }
}

I think it might be related to: https://github.com/mbedmicro/mbed/issues/840. It seems KSDK SPI peripheral (although iirc K20 uses the same one) has some timing issues with current code. Should get a seperate bug report on github.

posted by Erik - 11 Mar 2015

ceri clatworthy

9 years, 8 months ago.

not sure, but in PIC (wow a long long time ago)

you set mode 0..3 or 1..4

look at SPI Mode

Ceri

posted by ceri clatworthy 20 Aug 2014

SPI mode only affects the SPI clock line though ;). Generally the SPI data line is dont care outside the SPI packets.

posted by Erik - 20 Aug 2014

Michael Koster

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9 years, 8 months ago.