Adam Smith wrote:
>
> So I can handle the memory and the output fairly easy using the methods
> described for them, but I'm not so sure what to do about the first one.
> My chip of choice right now is a 16F872.  I was considering going for a
> 16F873 which has a USART peripheral and a little more program space but
> is double the cost.  I was thrown off, however, when I was reading the
> error rates in its data sheet; it says about 6%.  I need it down to 0.1%
> or 0.01%.

First, a 16F873 isn't "double the cost" of the 16F872, at least not so
far as I can tell. "1.5x the cost" would be more accurate. Still a
significant difference, though.

The error rates you're talking about are the difference between the
theoretical bit rate and the one that you get from the BRG. It is true
that the error can be significant if you're using one of the "standard"
clocks (4 MHz, 20 MHz, etc.). You can reduce the error to zero for the
usual serial rates by using a non-standard clock frequency of 3.6864
MHz, or 2x or 4x that frequency. If your serial communication is PIC to
PIC, don't worry about the errors at all, since they will be the same at
both ends of the connection.

A bit rate generator error of 6% doesn't mean that you'll see an error
rate of 6% when receiving characters! If the connection is short and
noise-free, you would probably see no character errors at all. However,
the noise immunity of your connection would be poor. I've heard varying
advice on what amount of error is acceptable, but you certainly want to
keep it low, say 2% or less.

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