On Wed, 31 Dec 1997 17:53:53 -0500 "Jason R. Williamson"
<jrwill01@STARBASE.SPD.LOUISVILLE.EDU> writes:
>I am using a PIC16C74A and the built-in UART feature.  I am trying to
>interface to a PC Serial Port (standard RS232).  However, I don't know
>if the PIC outputs are at RS232 or TTL levels.  I suspect the latter,
>but I haven't seen anything in the data sheets definitively either
>way.
>
>Do I need a RS232 level-converting chip?  What kinds are out there and
>what kind do you recommend?


        Yes, the 16c74a uart has TTL I/O.  It idles in the MARK (or 1)
condition of +5V.  You need to invert and level convert.  The classic
chips are the 1488 TTL to RS232 converter and the 1489 RS232 to TTL
converter.  There are various transceiver chips available now, some of
which include charge pump to generate the higher positive and negative
voltages.  Check out Maxim, among others.

Harold