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

Yes, the RS232 standard. This is a standard originally set up for computer
equipment to talk to modem equipment, and has become the defacto voltage
interface specification for serial interfaces that connect outside computer
cabinets. There are other standards, but this is the generally the
commonest.

>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?

So does the UART inside a PC. There are other chips that do the conversion
to RS232 voltage levels, just like using a MAX232 with a PIC.

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