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'[PIC]:Is it possible to adjust internal osc to 3.6'
2001\12\06@010542 by Gennette, Bruce

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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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2001\12\06@074833 by Drew Vassallo

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How about making a small program that simply changes the OSCCAL value when
you depress a button.  Each button press could decrease the value by 1 (or
whatever) and measure the CLKOUT until you get 3.686 or whatever you want.
Then by knowing how many button presses it took, define that value for the
OSCCAL and reload it.

--Andrew

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2001\12\06@125808 by Douglas Butler

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Serial comms with 1 start bit, eight data bits, and one stop bit aren't
that fussy about timing.  It automatically resynchronizes at every stop
bit/ start bit transition, so the message length doesn't matter.  In
theory you could be off by 10% and it would still work.  The character
length matters, so if you use 2 stop bits or fewer data bits the timing
is even more forgiving.  In practice I wouldn't drift farther than +/-5%
worst case, +/-3% is better.

Are you using a hardware or software UART?

Sherpa Doug

> {Original Message removed}

2001\12\06@185610 by Josh Koffman

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Scott recently was talking about accumulator registers...maybe that
would do the trick for you.

Josh

"Gennette, Bruce" wrote:
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2001\12\06@223504 by mike
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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.
On Thu, 6 Dec 2001 16:15:04 +1100, you wrote:

{Quote hidden}

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