piclist 2003\02\22\163902a >
Thread: Pin won't turn off properly
face picon face BY : Jinx email (remove spam text)

> BUT I do have to question the logic behind adding
> nops to a RMW, if you can afford one or more
> instructions timewise why not just movf,w then
> movwf PORT and write to the entire port??
> Or is there some esoteric benefit to clinging to
> a bsf PORT,x when you have cycles to spare??
> -Roman

In this particular case using a shadow register would slow
things down too much. Partly this goes back to the maths
in the PIC which generates the data that the SX uses. The
16/32-bit division/multiplication creates timing segments
in 4-cycle or multiples of 4-cycle blocks, sent to the SX as
9 bytes of data

The r-m-w code anomaly that caught my attention has been
re-written so that only one pin at a time is accessed, using
setb nop nop clrb, which fortunately is working (subject to
tests) for the timing-critical part of the code. The original
problem was during the handshake phase. I've added one
more handshake from the SX to the PIC and allowed 4us
for the PIC to turn off its lines. This in effect puts a full stop
on the comms and so the SX can move on the timing and
pulsing portion of its code, unencumbered by pinging the
handshake line

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<001b01c2daba$a8b1ec00$4789a7cb@joe> 7bit

See also: www.piclist.com/techref/ubicom/devices.htm?key=sx
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Subject (change) Pin won't turn off properly

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