Yes, I am aware of the importance of using a crystal. However, in this case, it is not possible. After I relealized what was probably happening I started programming the 509 without first erasing it. Those parts work fine. In fact I have used the internal oscillators in many other applications involving serial data up to 9600 baud without any problems. But that was always with parts that have a "precision 4 MHz" oscillator. Any project that would be subjected to large tempature extremes would certainly require a crystal.

So, back to my original question: How do I alter the value in the OSCCAL register?

Mark