"Richard Clark" wrote in message
...
Which is no more complex than setting 4 register bits - I wouldn't
call that a "routine," however.
-- I've
even written a few. :-)
Why more than one? Were the rest undersampling routines?

These were software RS-232 receivers, so you make use of whatever timers, edge
interrupts, etc. that you have sitting around to first the start bit, load up
a timer to then trigger in (what should be) the middle of the bit time for the
sample, etc. I've written pretty much the same routines a small handful of
times on different CPUs and in different languages.

The first ones I wrote were on ~1MIP CPUs in assembly and were limited to
about 2400bps full-duplex if you were also trying to run a reasonably
responsive terminal emulator (e.g., wanted to still have 50% of the CPU
available for the emulator), whereas more recently I've written them on ~20MIP
CPUs in C and can easily do 9600bps full-duplex with only a small impact on
CPU usage.

---Joel

On Wed, 25 Mar 2009 14:45:33 -0700, "Joel Koltner"
wrote:

These were software RS-232 receivers, so you make use of whatever timers, edge
interrupts, etc. that you have sitting around to first the start bit, load up
a timer to then trigger in (what should be) the middle of the bit time for the
sample, etc. I've written pretty much the same routines a small handful of
times on different CPUs and in different languages.

Hi Joel,

Pretty deep in the basement, there. Sounds like the way Apple used to
run their floppy disc, read it, and write it with a minimum of parts
(and expense).

73's
Richard Clark, KB7QHC