> Could anybody explain to me why the program EEPROM on a 16c84 needs
> 12-14V to be programmed when the data EEPROM can be written using normal
> voltage? It it two different types of EEPROM?

It appears that--at least with the current devices--the 16x84 uses VDD for
all the programming power requirements and it would be probably be trivial
[for Microchip] to modify the design of the chip so as not to require VPP.
There are at least three reasons they have not done so:

[1] The programming-mode entry algorithm, on which /MClr is raised to +12,
    is the same as the other parts; were some other method used to trigger
    programming mode, it would be harder to make a 'universal' programmer
    for the serial-mode parts.

[2] In most target applications, unless in-circuit programming is part of
    the app, there isn't really any way /MClr is going to be raised much
    above VDD; as a result, the programming is immune to glitchies and such.
    If conventional logic levels were sufficient to program the device, it
    may be succeptible to accidental erasure/scrambling.

[3] By making /MClr a three-state input (low, high, very-high) Microchip
    makes it possible to use all the pins on the device (at normal logic
    levels) in any combination, without accidentally triggering program
    mode.  By contrast, some other devices may enter programming mode
    erroneously if some of the so-called "general-purpose" I/O pins happen
    to have the wrong values on power-up.