I`ve got my SX sitting here now running quite hapily connected directly to
both lines, sending and recieveing fine. I checked my serial port and they
are true RS232 levels so I was quite supprised it worked. Especially as it
is running through around 4m of cable.

Wouldn`t recommend it for anything other than a quick lash up tho :-).


----- Original Message -----
From: Peter L. Peres <plp@ACTCOM.CO.IL>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, June 27, 2000 10:28 PM
Subject: [PIC]: not so [OT]: RS232 level (sort of) without 232 chip


> Hi,
>
> you don't need diodes, you need a 10K resistor for the incoming data
> (towards the chip) and a 220 ohm on the outgoing (from the chip). If your
> application is low current or sleeps you also need a zener or other
> clamping device across the micro power supply. I certify that this works
> up to 9600 Bauds at least ;-). You can use the same pin for Tx and Rx and
> save a resistor ;-) I can also certify that certain renowned PLL chips and
> other I2C peripherals do not like the -0.6V appearing on the input pin at
> all, and behave strangely, so your mileage will vary. Again:  PICs will
> work like this, but other micros may not.
>
> Peter
>
> PS: If you reduce the input resistor from 10k to ~3k3 then it can also
> power the PIC temporarily (hint: set break state on RS232 and wait for
> filter cap across PIC power pins to charge...). You HAVE to use a clamping
> device for this. 5V6 Zener (0.25W low leakage) will do fine.
>