AVR-Chat

At 12:59 PM 2/09/2005, you wrote:
> > >Witness RS-232-C and IBM,for example.
.......................
>    Why would I have had an RS-232 intercae connected?  I was reading a
>bank of pushbutton switches.

Thousand apologies :-[

You did mention RS232 and having to reverse the logic...
so I ASS U MEd (mainly me in this case :-) )....but you will
be surprised how many people connect RS232 DIRECTLY to the
UART and wonder why is doesn't work. This comes in a way
from some micro controllers that allows you to reverse
the polarity of the signal from the UART giving you in
effect a 5V RS232 port which does work in many modern
PCs but would create smoke in an older RS232 link
which IIRC may go as far as +-25V.

As far as polarity convention I always ASS U ME (that
word again) that we talk about positive logic UNLESS
the manual refers to negative logic. i.e. in/out of
the UART is positive logic whilst the physical RS232
link is in fact negative logic where a positive logic
signal represents a 0.

Have we strayed enough away from the original topic
yet or shall we do a bit more? :-)


Regards

John Samperi

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