RS232 communication with a MAX 2 CPLD

You need an external clock source with sufficient stability, typically a crystal oscillator. In my example, I'm using a 6 MHz crystal oscillator. MAX II has an internal oscillator, that can be accessed my a MegaFunction, but has only a roughly defined frequency and isn't suitable for UART communication. You would need an individual calibration at least, and there's no specified stability over temperature or supply voltage variation.