What determines how many bytes a 8451 reads during a SPI transaction?

[Kaspar]

Hello,

  What determines how many bytes a 8451 reads during a SPI transaction? Depending upon the device that you are interfacing with the quantity of bytes that comes back varies.

Regards,

  Kaspar

[Kaspar]

Hello,

   I have oberserved that the NI-8451 returns a byte during a read for each byte that was written, So if you write 5 bytes, you will get 5 bytes back. If you write one byte, then you will get 1 byte back. However, I have looked at the SPI clock with a scope and have noticed on 8 clock cycles for a btye arite, followed by a 1 byte read, so should there be 16 clocks?

Regards,

 Kaspar

[Anna_M]

Hi Kaspar,

What you described regarding the reading and writing of data from an SPI device looked correct - I posted a similar response on your other thread here.  Also, you are correct that each bit of SPI data will be transferred per clock cycle.  So, if you were to write a byte of data and then read a byte of data, you would expect to have 8 clock cycles per byte.  Hope this helps!