> If the duty cycle will be variable, you have 5 input lines to specify
> 1 of 32 possible conditions.  If your needs are even more complex,
> it's easy enough to clock in serial data

One way I'm looking at is to use a 4-bit parallel transfer and connect
the two chips' INTB0 together. INTF in each can be used as as flag
that data is ready or has been picked up

>If you're changing the PWM settings a lot, this probably wouldn't be
> a good solution

For any cycle you have at least 50% of the time available to look for
update data, more if you identify which, if either, state is on for longer.
The rate of change then becomes the issue. Do you wait until the
current cycle is finished or segue into the new frequency or duty cycle ?
This would depend on the smoothness required of changing from one
to another (for example smooth control with pot control going from
slow to fast)

Another possibility could be to generate analogue voltages to control
something a VCO like the ICL8038. Filtering would smooth out the
digital steps and probably give good results

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.