Problem in initializing SPI with ST32L476xG

Electronics and hardware Components
1

We are trying to initialize SPI on STM32L476xG with STLink Nucleo L476RG.

I am checking the ‘SPI_SCLK’ signal through oscillopscope, but not getting any output. Could someone please help me with this? If am doing something wrong here?

Here is the code:

#include “mbed.h”
#include “LSM9DS1.h”
#include “mbed_power_mgmt.h”

const PinName spi_MOSI = PinName::PA_7;
const PinName spi_MISO = PinName::PA_6;
const PinName spi_CLK = PinName::PA_5;
const PinName spi_CS = PinName::PB_6;
SPI spi(spi_MOSI, spi_MISO, spi_CLK);
DigitalOut cs(spi_CS);
short spi_addr;
short spi_data;

int main()
{
     //SPI config. 
     cs = 1;

     spi.format(8,3);
     spi.frequency(1000000); //1MHz

     printf("SPI Master Initialized \r\n");
     cs = 0;         // The SCLK should be working when the chip select is low.

     while(1) {
        spi.write(0xFD);
    }
    cs = 1;

    return 0;
}

Please could you let me know if am doing something wrong here? Or what could be the potential issues?

Thanks!
Regards,
Rohan

2

I think you will only get the clock signal output on SCLK if you invoke a spi.write() or spi.transfer, i.e., only when you’re actually transmitting data. Try sending a few dummy bytes in a while loop after pulling cs low and see what happens.

2 Likes
3

Thanks a lot for your response! I tried it, and have edited the code (as in the original post). But still not able to observe an SPI clock.
Also, as I just observe that the interface is SPI3 (and not simple SPI). Does that affect how am programming in any way?

4

Hmm. The code you provided seems to be alright. As shown on NUCLEO-L476RG | Mbed, the PA_7,6,5 pins refer to SPI1, not SPI3? Can you double check which pin on the Nucleo board you’re using / measuring?

1 Like