> Why does pc com port use RS232, is there a standard that requires 
> this.
> 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?

RS232 is intended for intercommunication between pieces of equipment 
over distances liable to be found in a computer room. The interface is 
intended to be reasonably robust and reasonably well protected against 
real world conditions.

Inter-Integrated circuit interfacing is done at a level that makes 
most sense for the technology in use, whether TTL, CMOS, ECL or 
whatever. The interfaces are (hopefully) robust enough for their 
intended on-PCB environment. It would make little sense to invariably 
engineer them for "real world" environments - especially so when many 
are used only within the PCB environment.

When there is a need to transfer signals between real-world and PCB 
environments suitably engineered interfaces are provided. These may be 
simple and passive and use only eg resistors and capacitors or may be 
more complex and may use special ICs or isolation equipment. When it 
is necessary for a PIC (or any other processor) to talk RS232 an RS232 
interface is added. similarly RS422, 20 mA current loop or any other 
specific standard interface. If a PIC was equipped with an RS232 
interface and one wanted to use RS422 it would be even more annoying 
than it is now to do so.

Using the right thing in the right place and knowing which is which is 
part of what engineering is about.



        Russell McMahon



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