> Hi, I am wondering if a RS232 driver IC like the MAX232CPE is needed
> for a serial communication (UART) with the computer? I am currently
> using a pretty new PIC18F452 microcontroller.

Yes, you need a converter.  The PIC signals are 0 to 5V.  The RS-232
signals are minimum -3V to +3v and inverted from the PIC signals.

> I notice that some circuit design out there interface the Tx/Rx pin of
> older PIC like the PIC16/17 directly to the serial port of the computer
> via a resistor. Why is it that they do'nt need the RS232 driver?

With a software UART, you can make the RX and TX PIC signals have the same
polarity as RS-232.  Many RS-232 receivers will work with 0-5V incoming
signals, but note that this is out of spec and certainly not universal.
The other direction apparently counts on the PIC clipping diodes and the
resistor to limit the signal to 0-5V.  All in all this is a bad idea.


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