You can try it with 3 volts, but you would probably be lucky (haven't tried
it myself). You will probably have to use 5 volts.  However, after that it
is easy enough. Just run the output of the PIC to an inverter (74HCT04 or
similar) and vice versa with the PC. The transmit portion of the PC should
be tempered a bit (values can get high) so put a 22 k resistor from pin 3 of
the 9 pin to your PIC input.

Of course, you don't have to use an inverter if the 3.0 will trigger the PC.
Just use the 'INVERT' key word when opening your port with CCS C.

#use delay(clock=4000000) // necessary for the 'rs232' directive
#use rs232(baud=9600, xmit=PIN_B0,rcv=PIN_B1,parity=n,bits=8, invert)

Dan

----- Original Message -----
From: Dan Rosenfeld <drosenfeld@SMARTMATTER.COM>
To: <PICLIST@mitvma.mit.edu>
Sent: Sunday, September 19, 1999 10:54 AM
Subject: rs-232 w/o level convert?


> Hi all,
>
> From looking at the archive, I can see that this is a somewhat FAQ.
> Unfortunately, I'm having trouble assembling all that I've read into a
> coherent picture applicable to my simple problem....
>
> I'd like be able to send characters (debugging printfs) from the 16LF84 in
> my circuit to my PC serial port W/O USING A LEVEL CONVERTER CHIP. I only
> need this to work on my PC for debugging purposes (it's not a production
> circuit) and at low baud rates and short cable distances. I'm also
wondering
> whether I can get away with running this all at Vdd = 3.0V (thus the LF84)
> or will I need run at some higher voltage while debugging.
>
> I'm pretty clear on the PC side (terminal emulator app or basic program),
> but I'm not certain of the exact electrical connections on the pic side.
> I've seen mention of using anywhere from 1k to 1meg in series w/o tx/rx
> lines and along with some mention of pulldowns on these lines.
>
> Also, do I need to do anything special with any of the other rs-232 lines
> such as RTS/DTS, etc. or can I just let them float? (Assuming the pc
> software is configured correctly.)
>
> So, what's the *exact* wiring/circuit that I should use here ?
>
> (BTW, inside the PIC I'm planning on using the CCS compiler's serial IO
> routines.)
>
> Thanks in advance,
>
> Dan