At 05:19 AM 5/13/2005, Jan-Erik Soderholm wrote:
>kenasw@btinternet.com wrote :
>
> > Why does pc com port use RS232,...
>
>To be able to communicate with *other* equipment with
>serial (RS232) ports, of course.
>
> > is there a standard that requires this.
>
>Yes. And guess what,  the standard is called "RS232"...

Careful.. Nothing requires that the PC use RS-232, other than the 
fact that a lot of other equipment uses it too.
232 was originally intended for industrial equipment in very noisy 
environments, like a steel mill.
It only went to 9600 baud IIRC, and 25' distance.

232 was used by most of the early computers, because it was 
relatively simple, and companies like Zilog made the SIO-0 which was 
a two channel UART, and a very nice one at that.
The PC's parallel port grew more or less out of an intel PIA chip 
(parallel interface adaptor), though similar implementations had been 
done for years on the Zilog PIO chip,. and other similar devices.

Apple used RS-422 or 485, I forget which, which was maybe a more 
sensible standard, but it never caught on outside their little enclave.
This is another serial comms standard, also intended for industrial use.

> > On the other hand, why do the pics use uart without rs232,  is this
> > a pic problem which will make it more complex to connect to pc?
>
>Very few (if any at all) uart's has RS232 builtin. Today the RS232
>interfacing is done with chips like the MAX232.

Max 3100's are available with the 232 drivers built in. It's an SPI based uart.


-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist