The RS-232 spec indicates that between -3v and 3v is no man's land for a valid
RS-232 signal.  3-12v and -3 to -12v are ok.

However, the vast majority of hardware UARTs produced now let 0v (gnd) fall into
the -3v to -12v range.  Thus the effective range of most RS-232 receivers is -12
to 1v and 3v to 12v.  So 0v and 5v are valid signals.

You will commonly see hobbyist circuitry which drives the recv line of RS-232
directly from the micro, and accepts the TX line of the RS-232 port through a
resister (and clamping diode) directly to a pin on the micro.  Since the PIC has
internal clamping diodes you will run across RS-232 PIC interfaces that use only
one resister.

-Adam

Russell Farnhill wrote:
>
> Hi,
>
> I've Been playing around with some serial routines on a F84.
>
> With the PC serial RX pin connected direct to the TX pin on the PIC
> I can seemingly reliably receive serial data using Hyper Terminal.
>
> I thought that a MAX232 chip or similar was needed to send 5v serial data
> to a PC. Is this just a fluke or am I missing something here ?
>
> Thanks,
>
> Russ.
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.