Ah! you are right.  The position within the loop of the reads and writes
only affects latentcy, not uncertainty.  Sorry about that.

I am a C programmer (CCS PCB).  To get better than the obvious few
assembly instructions will require someone more familliar with the
quirks of PIC assembly code than me.  I am actually comptemplating my
first project that will require some assembly embedded in the C.  I will
have to write the code, count the cycles, THEN choose the crystal
frequency.  I have to generate exactly four cycles of exactly 300kHz
with complementry outputs.

Sherpa Doug

> -----Original Message-----
> From: Dan Lanciani [mailto:ddl@DANLAN.COM]
> Sent: Friday, February 08, 2002 3:09 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: minimum uncertainty input->output
>
>
> Douglas Butler <dbutler@IMETRIX.COM> wrote:
>
> |The obvious solution to both latency and uncertainty is an
> external AND
> |gate.  When you want the signal propagated you just turn on the AND
> |gate, and turn it off when you want to stop.  Latency is the delay of
> |the gate and uncertainty is nil.
>
> I'm not trying to design a circuit.  I'm trying to determine
> the best that
> the firmware in an existing design could be doing.  There is
> no external gate.
>
> |If you must do it in software look at what clock phases the
> bit test and
> |set operations work on.
>
> Could you expand on this?  It isn't clear to me how that
> timing would affect
> the uncertainty.
>
> |Sherpa Doug
> |
> |> -----Original Message-----
> |> From: Dan Lanciani [mailto:ddl@DANLAN.COM]
> |> Sent: Friday, February 08, 2002 4:11 AM
> |> To: PICLIST@MITVMA.MIT.EDU
> |> Subject: [PIC]: minimum uncertainty input->output
> |>
> |>
> |> Given a 16C54 class device, what is the minimum
> |> uncertainty/jitter with
> |> which a change in a general input can be propagated to a
> |> general output?
> |> My first thought is that a bit test & skip/goto loop gives a
> |> three instruction
> |> cycle uncertainty, but I'm probably missing a trick.  I don't
> |> care (within
> |> reason) about minimizing the latency, just the absolute
> |> uncertainty in the
> |> latency.
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>
>
>

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.