Chaipi Wijnbergen wrote,

>I am developing a small project using the PIC 16C74 and recently
>needed to change the Crystal from 16MHz to 20MHz. When I did
>that, a problem started with the asynchronous communication
>controller, it started to recived wronge characters.

 Check out pages 2-600-607 of the MC 1995/96 Databook. It's the
 section on the (SCI) module, which has a formula for baud
 rate error and information on the registers etc.

                                  Mike