SPI read and write

[ToTo]

Dose this capture from the Nordic Specification means that to read bytes from SPI i need to send before. Each byte i send i get a byte!!! MLy case i have read only sensor that sends periodically. If it is mandatory to send in order to receive so i have to send 4 bytes to receive the 4 bytes i am looking for.11.PNG

[Jørgen Holmefjord]

Hi,

SPI is typically implemented using shift registers, meaning that data is clocked out of the master shift register and into the slave register through the MOSI line, and similarly, out of the slave shift register and into the master register through the MISO line.

In theory, you should be able to clock in the data through the MISO line without having the MOSI line connected. You are still required to "send" dummy data from the master, to make the clock run.

This operation will depend on your sensor. Could you provide details on the device? Then I might be able to help you with your setup.

Best regards,

Jørgen

[awneil]

Yes, this is a typical implementation - not just some strange Nordic "funny".

This is because the SPI clock is always generated by the Master and, typically, the way to get the Master to generate its clock is to send something.

en.wikipedia.org/.../Serial_Peripheral_Interface_Bus