In my application, the PIC is slave so the clock is coming from the Vector2X compass at a fixed 4kHz rate. Accelerating the PIC's clock would, in my opinion, allow more instructions to get executed between each incoming bit (or byte). With such a slow SPI clock rate I assume the PIC should have lots of time to spare between bytes. Anyhow the problem doesn't seem to be clock related... For your information, is the complete setup : Vector 2XG digital compass as a SPI master, it's 4 kHz fixed clock coming into a PIC 16F877's SCK in slave mode. - The PIC polls the compass to get it's 16bit heading and sets a flag to prepare for the first incoming byte (MSB) - PIC raises SPI interrupt after first byte has been buffered, buffer is saved/emptied, flag is updated for next incoming byte (LSB) - PIC raises SPI interrupt again after the second byte has been buffered, buffer is saved/emptied, flag is reset so the cycle can start over. - While all the interrupt stuff is taking place the PIC continuously updates a led display with the saved values. Tobie Horswill ----- Original Message ----- From: "K|bek Tony" To: Sent: Wednesday, September 20, 2000 9:52 AM Subject: Re: [PIC] : SPI doing a right-shift ? If this would work I'm very perplexed, then I guess all bet's are off :-) As the SPI clock is actually RELATIVE to instruction speed ( and Xtal ). So replacing an 8Mhz with an 4Mhz would ( without sw change ) slow down the SPI clock speed by an factor of 2 BUT ALSO the instruction speed with the same amount. I'm curios how excately you are using the SPI, can You post the relevant snippet ? -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics