You don't need to mess with oscal, nor use a specific clock, assuming
you're using bit-bashed RS232.
It is not particularly difficult to auto-detect the baudrate of an
incoming signal, as long as you know what initial character you are
expecting (a zero byte is best, as it has maximal length), and then
adjust the timing of your tx/rx code to compensate.=20

On Thu, 6 Dec 2001 16:15:04 +1100, you wrote:

>For short messages I think it should be possible to implement simple, =
low
>speed (1200/2400) RS-232 in chips that have an internal 4MHz (nominal)
>oscillator *IF* the osccal can be loaded with a correctly calculated =
value.
>At these low speeds it should be possible to identify and synchronise =
with a
>start bit and then read in a few bytes before losing synchronisation.  =
If
>messages are restricted to that size comms should be possible.
>
>Does anyone know if osccal can be adjusted to slow the chip down by =
about 8%
>(((4-3.6864)/4)*100) ?
>
>If it can, what is the formula to calculate the osccal value from the
>factory supplied osccal adjustment value ?
>
>If it can't what is the formula to 'drop' cycles to simulate 3.6864MHz =
when
>the chip is operating at 4MHz ? (nop every 12.5 instructions ?)
>
>Thanx in advance.
>Bye.

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