Dumitru, you're very good documented.

http://www.surducan.netfirms.com/RS232.html
Vasile

On 1/12/07, Dumitru Stama <list@mirosat.com> wrote:
>
> 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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