Don McKenzie <donmck@tbsa.com.au> wrote :

>
> I hope I'm not missing the point on your 16Cxx in-circuit
> programming question, but why would you need to program anything
> but an 84 in-circuit?
>
> Please sit me back in my corner if I am way off the mark.   :-))
>
> 1)  An EEPROM chip: Fine. Load and go!
> 2)  An OTP chip: No, why?

For much the same reason as the EEPROM : you can load the code in at
the last possible moment, even if you only get one chance to get it
right. This has lots of advantages in a production situation :

 - customisation (e.g. serialisation) of products
 - single manufacturing process for software variants
 - minimising inventory control of preprogrammed parts
 - minimising rework costs after software changes
 - minimising handling of components (especially worthwhile for SMT)
 - possible programming of parts in an in-circuit-test fixture

The move toward in-system programmable parts is mostly driven by these
advantages, which maximise the advantages gained by suffering the
slightly higher cost of programmable parts (over mask-programmed parts).
The usefulness of these devices for the low-budget user is something
of a (desirable) side effect.

-adrian