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'12Cxxxx Serial'
1998\10\11@210503 by miked

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Anyone tested how reliable the 12C parts are for serial
communications using the internal RC oscillator?
Mike DeMetz N9GEZ
Elkhart, IN
spam_OUTmikedTakeThisOuTspamelkhart.net
http://www.elkhart.net/~miked

1998\10\11@213944 by James Cameron

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Mike DeMetz wrote:
> Anyone tested how reliable the 12C parts are for serial
> communications using the internal RC oscillator?

No, but I'm ready and willing to find out.
Unfortunately I don't have EPROM versions, only OTP.

In the case of the 12C509, there is no interrupt system, so any timing
would have to be done in delay loops or using the instruction timer.

If I thought about it long enough, I could compare the extremes on the
R/C oscillator calibration graphs in the data sheet, and work out what
the divergence from a baud rate would be at the supply voltage I was
using.

Hey, a thought; listen to an incoming data stream, work out how far off
the beam our oscillator is, and apply new OSCCAL values accordingly.

--
James Cameron                                    (.....cameronKILLspamspam@spam@stl.dec.com)
Digital Equipment Corporation (Australia) Pty. Ltd. A.C.N. 000 446 800

1998\10\12@085957 by Peter L. Peres

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On Sun, 11 Oct 1998, Mike DeMetz wrote:

> Anyone tested how reliable the 12C parts are for serial
> communications using the internal RC oscillator?

I did not test that but I do know that normal async 8n1 requires 5% clock
accuracy on both sides. Shorter words can live with less accuracy (e.g.
BAUDOT 5 can live with 7.5%) under the same conditions.

The OSCCAL need not be used to calibrate a software loop, the loop itself
can be calibrated in 1usec increments normally (at ~4MHz).

Peter

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