Ed Brown wrote:
.....
 Selected PIC for this project is
>an 'F877.  I had hoped to spurt SPI data out as a very fast stream,
>concurrently building the packet frame,
........
>My problem is this:  Using PICC, I have written simple minded code to
>generate data so I can see if the PIC can keep up.  RS232 seems to be able
>to, but [[[I have seen very long latencies between SPI words (operating at
>CLK/4)]]].  Is this normal?  If these can be shortened, how and how much?
........


Hi Ed,

Not sure if this will answer your question, but FYI ---

I interfaced a 12-bit 400 khz SPI A/D [LTC1400] to a PIC 16C76
operating at 20 Mhz. Writing in assembler, the very fastest I
could get the PIC to convert the A/D using the built-in SPI port
was about 300 khz. This required doing 2 8-bit SPI xfers/sample,
plus data storage/indexing while the SPI port executed. If you
are only doing 8-bit xfers, however, it should go about twice as
fast.

I could not squeeze out a faster rate from the SPI. I used
clock = OSC/4 with the 20 mhz xtal. However, just checking the
SSPCON register info in the d/s, I see it is possible to use
clock = TIMER2_out/2, which I did not try, and which may allow
faster operation.

hope this helps,
- dan michaels
www.oricomtech.com
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