I'd suggest a small improvement, to limit the input voltage from the PC's
TX line:

 TX<(2)--(2)-/\/\/\/-------------+-----/\/\/\/---+--/\/\/\/----+
              10k                | X     10k     |    40k      |
                          | /|   |  | /|         |            ///
         	  +5V  <--|< |---+--|< |---+     +---- RB0
                          | \|      | \|   |
                                          ///

When TX goes high, the voltage in node X is equal to 5.7V so the voltage
on RB0 is equal to 5.7V*4/5=4.56V. No danger for PIC at all !!!
Similarly the diode/voltage divider can limit the reverse input current 
(however it is a little more difficult to explain - consider the
Shockley's equation ;-) ).

					HTH
					Wojciech Zabolotny
					wzab@ise.pw.edu.pl

On Mon, 3 Apr 2000, [Iso-8859-1] Kübek Tony wrote:

> Some designs for RS232 interfacing:
> 
> ; Simple RS232C - PC to PIC Interface     Aug/94      T. Rudersdorfer,
> AScT
> ;  revised Sep/94
> ;
> ;   1 - 470 ohm   short circuit current limit
> ;   1 - 10k       open collecter pull down
> ;   1 - 47k       power up pull up
> ;   1 - 470k      injection current limit
> ;   2 - 15pf      oscillator stabilization
> ;   1 - .1uf      decouple PIC and regulator
> ;   1 - 10uf      voltage stabilization
> ;   1 - 5.0688MHz standard communication xtal
> ;   1 - 1N4150    reverse voltage blocking diode
> ;   1 - 78L05     5V low power regulator (100mA Max)
> ;   1 - 16C84     PIC
> ;   1 - LED       do something test led
> ;   1 - 2k7       do something current limit for test led
> ;
> ; PC  DTE  DCE
> ;
> ;  RX<(3)--(3)-/\/\/\/-----------------------------+--/\/\/\/----+
> ;                470                               |    10k      |
> ;                       |\ |                       |            ///
> ;        +-----/\/\/\/--| >|---------------------+ |
> ;        |       2k7    |/ |   ---------------   | |
> ;        |              LED   | 1     U   RA1 |--+ |
> ;        |   ^ +5V            |           RA0 |----+
> ;        |   |                | ____  1  Osc1 |------------------+
> ;        +---+-/\/\/\/--------| MCLR  6  Osc2 |------+           |
> ;                47k    +-----| Vss   C   Vdd |--+   |     _     |
> ;                       |  +--| RB0   8       |  |   +---||_||---+
> ;                      /// |  |       4       |  |   | 5.0688MHz |
> ;  TX>(2)--(2)-/\/\/\/-----+  |               |  |  _|_         _|_
> ;               470k          |_______________|  |  ___15pf     ___15pf
> ;                                                |   |           |
> ;                  1N4150        _____    ^ +5V  |  ///         ///
> ;                   |\ |        |     |   |      |
> ; RTS>(4)--(4)-+----| >|----+---|78L05|---+------+
> ;              |    |/ |    |  1|_____|3  |
> ; CTS<(5)--(5)-+           _|_     |2    _|_
> ;              |           ___10uf |     ___.1uf
> ; DSR<(6)--(6)-+            |      |      |
> ;                          ///    ///    ///
> ; GND (7)--(7)-+
> ;              |
> ;             ///
> ;
> ; RS232 RX circuit background:
> ;    Based on AN521 in the 1993 Embedded Handbook; PIC I/O pins can
> handle
> ;    +/- 500uA of continuous injected current. This means voltages
> greater
> ;    than VDD and VSS CAN BE used as long as adequate current limiting
> is
> ;    provided. My original RX input design isolated the PIC by using an
> ;    extra transistor, diode and resistor. This can be eliminated by
> using
> ;    a large enough resistor value in series to the PIC I/O Pin. RS232
> ;    voltage levels can be up to +/- 15V, therefore, a 470k resistor
> provides
> ;    an adequate current limit of 32uA (the same current used in AN521).
> ;
> ; RS232 TX circuit background:
> ;    Researching specification sheets for RS232 receivers like the 1489,
> ;    reveals that they do not require bipolar voltages to operate. The
> ;    1489 in fact clips all -ve signals to ground, therefore only
> requiring
> ;    +ve and ground input levels.
> 
> Or have a look at the image at
> http://www.ise.pw.edu.pl/~wzab/picadc/picadc.html 
> ( on the middle of the page )
>