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'weird behaviour of a 16C84 ...'
1998\10\19@072022 by Stefan Sczekalla-Waldschmidt

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Hi,

While testing the code for a send only serial transmition from
a PIC 16C84 to a PC I noticed something realy odd behaviour of the
programm running on my pic.

It4s consist of a loop which just count4s  up a byte in the
range from D'65' to D'126' ( viewable ASCII ) and send this
char to the PC.

the byte is simply incremented with a "incf" instruction.

while testing once, I noticed that i got e.g. "AEIM ..." insted of
the expected "ABCDEFGHI..." - the byte seemed to be not simply
incremented, it was added with 4.

After resetting the PIC the PIC worked "normal" again.
( means sending "ABCDE... )

while I couldn4t make the PIC showing this odd behaviour again,
I4m still wondering how this could happen.

will evetually the incf opcode have the opportunity to increment by two
( caused by a erreanous bit in PGM memory ) ?

Any Ideas ?

1998\10\19@120524 by Peter L. Peres

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On Mon, 19 Oct 1998, Stefan Sczekalla-Waldschmidt wrote:

> while testing once, I noticed that i got e.g. "AEIM ..." insted of
> the expected "ABCDEFGHI..." - the byte seemed to be not simply
> incremented, it was added with 4.

I'm almost certain that by connecting a variable PSU to the PIC and
increasing the voltage very slowly from 0 you will be able to duplicate
this and other strange things ;). The PIC is not alone on this, it's the
state machine that implements the core in the PIC that can assume invalid
states if not reset properly.

Peter

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