Interestingly,
there is no ROM chip in a PCW. Part
 of the ULA acts as a
 tiny bootstrap ROM (it outputs the correct states
 onto the data bus
 depending on the state of the address bus), just
 enough to read the boot
 sector into RAM and execute it. 
  Holy freeholy Batman. Now that's a first for me. 
 
It something of a shock for me when I read the schematics (amazingly I've
never seen inside a physical PCW...)
[Serial/parallel interface]
   no idea where
you'd
 find one. 
  Gee thanks mate. Leave me hanging. Yes I was made
 aware of the interface. But for starters I think I'll
 need to worry more about hacking up a ribbon. As if
 I'd find the time...
  Contrariwise I guess it wouldn't be any big deal to
 create an rs-232* interface from scratch. I can dream
 can't I? 
 
AFAIKL there are no custom chips in it, it's jsut a bit of TTL, and
some standard peripheral chips. I can find out more (and find the pinout
of the bus connector) if you're serious about making one.
-tony