SPI MISO data is not reflecting on the receive buffer

Question

Attached the MOSI and MISO signal CRO captures. I could see the write and read data on the SPI lines. But MISO data is not reflecting on the receive buffer. 
 Image1

Image2

The Yellow line in the above picture is MOSI and Green is MISO. 
 Its is a combination of Read(Read Command + Start Address) and Write sequence (Write Enable, Write Command + Start Address, Data) 
 Image 1 Data is 0x50 
 Image 2 Data is 0x55 
 
 Yellow line (MOSI) Read Command is sent followed by read address ( 24 bit address - 0x00,0x00,0x00). And response for the received command is in green (MISO) line 0x50(image1) and 0x55(image2). Reading 4 bytes of data from starting location 0x00. 
 Yellow line (MOSI), Write Enable, Wrtie Command is sent followed by read address ( 24 bit address - 0x00,0x00,0x00) and four byutes of data (0x50 - (Image1), 0x55 (image2), Write status command. Response for the received command is in green (MISO) status byte .Â 
 
 Conclusion: Analysing both images, Even if write different data in the location (0x00) during the read sequnce i could see the same data (Data written in wrtie sequence) in the MISO lines but same data i am not able to capture in the receive buffer for the further processing. 
 Knidly share your thoughts in the same. 
 
 Thanks & Regards, 
 Chinnasamy.

Jørgen Holmefjord · Accepted Answer

Note that most SPI devices will output data after you are done sending the command/address/etc. The SPI peripheral on nRF52 devices will start filling the RX buffer simultaneously with TX buffer being clocked out. If you send 4 bytes and expect 4 bytes back after TX is done, you need to set the RX buffer size to 8, and discard the first 4 bytes. 
 Please have a look at the sequence diagrams in the SPI peripheral documentation

SPI MISO data is not reflecting on the receive buffer

Top Replies