>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>On Behalf Of Rich
>Sent: 27 July 2007 02:27
>To: Microcontroller discussion list - Public.
>Subject: [EE] Software SPI
>
>
>Has anyone created a software SPI?

SPI is trivial to bit bang compared with e.g. I2C.  However, note that there are four possible timing/polarity variations with SPI, and most peripherals only support one.  The data can be clocked on a positive or negative edge, and on a trailing or leading egde so you have to make sure you set up the data at the right point.  The PIC datasheets usualy have a diagram explaining this in the MSSP section.

For the highest possible speed, don't use a loop but clock out each 8 bits with separate instructions (i.e. unroll the loop).  This has only a small code size overhead but can give a good improvement in bit rate.

Regards

Mike

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