Assuming you want to either send or receive but not both at the same time,
I have done 38.4kbaud on 16c5X series with 4mhz (RC) oscillator. Of course,
having
a better clock source makes the code a bit easier. Are you sure you need
this to be
interrupt driven? What are you using the serial for? What are the constraints?

Cheers,
eric

>Has anybody managed to transmit and receive at baud rates of
>about 38k baud on a 10MHz 16C84?  I recon it's just about
>possible if using interrupt-on-change 7:4.  Anyone done it, do
>you have the code?
>Mark