Hello Andrew .

> I have just started with PICs and am using the PIC-Dem1 from Microchip with a
> CCS-PCM compiler and the 16F84 chip. I wish to send data from the  PIC to a PC
> via the RS232 port. I am getting data through to the PC serial port but it is
> garbled - the compiler suggests that this may be a problem with the RC
 oscillator
> in this demo circuit, i.e. you can not be sure of the exact frequency. I think
 all
> my port settings are OK. Does anyone have any suggestions or must I use a
 different
> circuit with a crystal instead .

To normal functioning (without garbage or so) baud deviation of RS-232C
should not exceed 10% limit (receiver baud to/from transiver) .

So if you "system" clock is deviated by +-5% (RC circuit) you will
satisfy RS-232C standart else (more than +-5%) you get a garbages .
In "else" case use a crystal osc .

To simplify connecting PIC to PC i apply AD232C
TTL<>RS-232C converter and i use following cable:

PC          PIC
===============
>-TxD-----RxD-<

>-RxD-----TxD-<

>-SGND----GND-<

>-RTS-+
      |
>-CTS-+

>-DSR-+
      |
>-DCD-+
      |
>-DTR-+
===============

WBR Dmitry .