I have been using rs232 without any handshake but calculations of
spbrg were my first mistake. I made a simple php calculator and this
is what i got for your 13.5MHz frequency :

The desired frequency is : 13.5000 MHz
The desired baudrate is : 9600 bps
--------------------------------------------------------------------------------
BRGH = 0 - Low Speed
The calculated value for spbrg is : 20.973
The value you will use for spbrg is : 21
The calculated baudrate for this value is : 9588 bps
The error is : -0.13%

BRGH = 1 - High Speed
The calculated value for spbrg is : 86.891
The value you will use for spbrg is : 87
The calculated baudrate for this value is : 9588 bps
The error is : -0.13%
 
The error is very small and you will be able to use 9600 with BRGH
being both high or low. Try (as already suggested) without a handshake
and see if it works. After this verify you connected CTS and RTS as
they should be connected.

wikipedia content below:
http://en.wikibooks.org/wiki/Serial_Programming:MAX232_Driver_Receiver

The levels should be :
     RS-232              TTL             Logic
-----------------------------------------------
 -15V ...  -3V  <->  +2V ... +5V    <->  high
  +3V ... +15V  <->   0V ... +0.8V  <->  low

The MAX232(A) has two receivers (converts from RS-232 to TTL voltage
levels) and two drivers (converts from TTL logic to RS-232 voltage
levels). This means only two of the RS-232 signals can be converted
in each direction. The old MC1488/1498 combo provided four drivers
and receivers.
Typically a pair of a driver/receiver of the MAX232 is used for
TX and RX
and the second one for
CTS and RTS.
There are not enough drivers/receivers in the MAX232 to also connect
the DTR, DSR, and DCD signals. Usually these signals can be omitted
when e.g. communicating with a PC's serial interface. If the DTE
really requires these signals either a second MAX232 is needed, or
some other IC from the MAX232 family can be used (if it can be found
in consumer electronic shops at all).


PL> Thank you for your replies.
 
PL> I'm using Sipex SP232ACT. 
 
PL> I'm using crystal oscillator. It might be problem with oscillator. I wanted to have PIC running at 40MHz on my board, but I didn't read the datasheet carefully ( yes, I know :-/ ) and instead of
PL> putting 10Mhz oscillator and using PLL I put 40MHz oscillator on the board. It is actually running at 13,3 Mhz now. 
 
PL> Do you think that it might be the problem?
 
PL> I'll try lowering the baud rate anyway.
 
PL> Sam
 
 
 

PL> ________________________________

PL> From: piclist-bounces@mit.edu on behalf of Jinx
PL> Sent: Fri 1/12/2007 11:00 PM
PL> To: Microcontroller discussion list - Public.
PL> Subject: Re: [EE] Very odd problem with RS232...




>> You may be getting out of sync with the PIC and the PC if the
>> frequency is off by more than a few percent.   Try lowering the
>> baud rate on both the PC And your PIC board, and see if that
>> makes any difference

PL> Lowering the baud rate will just make errors take longer to happen.
PL> If it is a timing problem, the PIC clock needs to be changed to match
PL> the baud rate from the PC

PL> Sam, are you going through an RS232 i/f (eg MAX232) ?

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