>
> Randy Walsh Wrote:
>
> >Need help with a little hardware RS232 inteface.
> >


> Myke Predko responded:
> Where you may have your problems is with the negative voltage generation.
> Your PC (like mine) may "read" 0 Volts as a "Mark" and actually require a
> negative voltage.
>
> There's a simple circuit for using the RX Negative Voltage.  Please
correct
> me if I'm wrong:
>
>
>
>              |
>              |     10K Resistor
>   PIC   RXIn |-----^^^^^^-------------------+-------------------- From PC
>              |                              |
>              |                              >
>              |                              < "Pull Down" Resistor
>              |                              >
>              |                              |
>              |                              +-------------------- To PC
>              |                              |
>              |           Resistor         |^
>         TXOut|-----------^^^^^------------|
>              |                            |\
>              |                              |
>              |                             +12 Volts
>              |
>
> This will send a Negative Voltage nominally and then send a Positive
voltage
> when the TXOut Line is High.
>

I like this idea of stealing -12V off the RX line.

Forgive my ignorance first, I'm more of a software buff than hardware, but
what if...the RX line is receiving while I'm trying to TX?  Will it's +/-
swing mess up my ability to get -12 volts from it?

Assuming this is true, and assuming I don't TX and RX at the same, then
when I leave the TXOut line low (not in use), the "To PC" line is sitting
at -12V  (Did I get this right?).

What happens when I receive a character from the PC?  It seams to me that I
will then get the same character sent back to the PC over the TX, only
through the pulldown resistor?  Is this correct?

As before, please explain in detail, as I said, I'm a little dense when it
comes to making hardware do its thing.


Thanks again.
Randy