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SPI CS length

Question asked by zied on Jan 6, 2012
Latest reply on Mar 15, 2012 by zied

I try to develop an adsp 592-A spi driver. Actually, I use mode 3 (CPOL=CPHA=1). To validate this work, I tried to connect to ezkit-lite (one master and the other slave). When I active the slave as a sender and the muster as a receiver, I can easily see with an oscilloscope that at high frequencies (SPI Baud between 2 and 50 ~ frequency in MHz) that the SPISS length is greater than the length of sent data. For example, if I use a SPI-Baud equal to 6, the SPISS is low two times the length of 1 byte. This problem will disappear otherwise.

In normal, the SPISS must be switched on high just after master reception of the fixed length. But in my case I found that the master switch on high the slave select after n time the normal time.

Is this normal.