SPI CS pin going High and From Transceiving function data is not coming.

[Madhu Mohan Reddy]

I am using nrf52840 and i am working on nrf connect sdk v2.6.0  in my overlay file SPI CS pin is low but it is going high between the communication.

Data is not receiving from the sensor using spi_transceive_dt() function but in logic analyzer the MISO and MOSI lines are working.

Please look into the below code and help me on this.

[Håkon Alseth]

Hi,

 

Your /CSN pin works as it should. Goes low when the transmission occurs, and back to idle level afterwards (ie. high level)

You need to adjust your sampling frequency in the saleae logic application, looks like it is too low.

Looks like you're sending one byte and receiving two. Can you share what you're sending and receiving?

 

Kind regards,

Håkon

[Madhu Mohan Reddy]

In spi_transceive_dt() first byte is dummy as per document so 2nd byte Iam reading but 2nd byte also coming from sensor is zero

when I increase SCLK frequency as 8 MHZ  it is showing like this and miso line is transmitting when CS pin is in high

Iam sending the command and receiving the sensor value using transferSPI function 

I am sending through uart values are not coming


Thank you.

[Håkon Alseth]

Hi,

 

If you look at the chapter I previously mentioned: Each transaction is 2 byte op_code, written from the nRF, and you will then get 'n' bytes returned based on the contents of the second byte sent. At this moment, you're writing 1 and reading 2 bytes twice, then clearing your /CSN pin.

 

Kind regards,

Håkon

[Madhu Mohan Reddy]

when I write 1 byte it will come 1 byte 
why I am asking in dev academy SPI lesson spi_transceive function transmit size is len  receive size is len + 1

thats why i am asking this 

thanks in advance

[Håkon Alseth]

I am not sure what you're asking. Could you elaborate on what you are actually stuck with?

You need to send two bytes, not one. The second byte holds the amount of registers to read, minus 1, as per the datasheet of the sensor.

 

Kind regards,

Håkon

[Madhu Mohan Reddy]

For Receivig the data from sensor I am sending only reg address ,for reading chip id I need RREG two bytes 

using spi_transceive function I want to send 1 byte and receive 1 byte output  values 

tx_buffer = 1
rx_buffer should be 1 or 2 ?

in nrf dev academy in spi lesson its mentioned that tx_buffer = len then rx_buffer = len +1.


thanks in advance 

[Håkon Alseth]

Hi,

 

Not all sensors are equal. You should have a look at the datasheet for your sensor and use that as a basis for how to communicate with the device.

Madhu Mohan Reddy said:

tx_buffer = 1
rx_buffer should be 1 or 2 ?

This is not correct for the specific sensor that you're interfacing.

tx_buffer should be 2 bytes and hold the register (OR with 0x20), and the second byte is the amount of registers to read, minus one.

 

Kind regards,

Håkon