Thank you both for your help, as it happens it was a miss calculation for
the baud rate, but your comments made me aware of a few things. Got it
working fine, thanks again.

Gavin

On Nov 20, 2007 3:55 PM, Thomas C. Sefranek <tcs@cmcorp.com> wrote:

> There IS a 4:1 difference between BRGH and BRG16.
> (High/ low speed baud rate generators)
> You didn't say which you selected.
>
>  *
>  |  __O    Thomas C. Sefranek  WA1RHP@ARRL.NET
>  |_-\<,_   Amateur Radio Operator: WA1RHP
>  (*)/ (*)  Bicycle mobile on 145.41MHz PL74.4
>
> ARRL Instructor, Technical Specialist, VE Contact.
> http://hamradio.cmcorp.com/inventory/Inventory.html
> http://www.harvardrepeater.org
>
> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of
> Gavin Dingley
> Sent: Tuesday, November 20, 2007 9:14 AM
> To: piclist@mit.edu
> Subject: [PIC] PC RS232 Interfacing to a 18F458 - problems
>
> Hi,
> I have only just started experimenting with PICs, and have
> breadboarded a circuit using an 18F458. The function of the circuit is
> to   display on 8 LEDs the binary of the ACII character sent from a
> PCs RS232 port (actually a virtual port from USB, i.e. one of those
> USB to RS232 connector leads).
>
> First I loaded the SPBRG register with 0x0D, based of the formula
> given in the datasheet:
>
> x = (Fosc / (BR * 64)) +1
>
> Fosc is the instruction clock frequency (i.e. the crystal clock / 4),
> BR is the desired baud rate, and x id the number to load into the
> register, so:
>
> x = (920e3/(1200*64))+1 = 13 = 0x0D
>
> Using a 3.68MHz crystal
>
> Now when I tested the circuit is seemed to operate best at a baud rate
> of 4800, rather than 1200, suggesting the frequency to use is not
> Fosc, but the actual crystal frequency.
>
> The second problem is that the binary patterns displayed on the PIC
> LEDs do not correspond to the ASCII of the typed character, and the
> virtual terminal on the PC is set to 8-bit transmission. Also,
> although the binary pattern is different for each character sent, even
> if it is incorrect, then LED representing the MSB of the port is
> always lit, regardless of the character sent.
>
> Now, either I still have the wrong baud rate, the character set used
> by the PC is not ASCII, or there is something I have completely
> missed. I don't think I am getting bit-rate and baud rate mixed-up
> here either, the terminal sets baud rate, not bit rate, and the
> datasheet I'm sure talks in terms of baud to.
>
> Thanks in advance,
>
> Gavin
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