[sdiy] SPI comms - how fast is reasonable?

[Tom Wiltshire]

Hi All,

Today I've been learning about SPI communications, and getting one  
PIC talking to another. For this I have a pair of 16F767's  
(transmitter and receiver). The receiver has an LCD attached to  
display data that it picks up. The idea is to use this basic test  
setup to get a protocol worked out for synth parameter data  
transmission. Once that is done, I'll have a known-good transmitter  
that I can then use to send parameter data to dsPICs. Doing the  
testing with a PIC and a dsPIC directly is a pain in the rear because  
MPLAB has to download a different OS into the ICD2 clone programmer I  
use every time you switch chips.

Anyway, I've got the basics running, but I'm currently running the  
SPI clock at 20MHz/64 = 312.5KHz. The chip can also run it at 20MHz/ 
16 which would obviously be preferable (why hang about?) but that is  
producing glitchy data. The datasheet says that 10MHz is possible.

What do I need to watch out for trying to send >1MHz (up to 10MHz in  
theory) SPI clocks and data around? Is it realistic to expect this to  
work on a breadboard?
How long can flying wires between transmitter and receiver be?

  I'd appreciate any experience/pointers anyone can offer to help me  
get SPI comms working as fast as is reasonably possible.

Thanks,
Tom