>
> Hello All,
>         I've been reading over the Easy PIC'n book and the impression he
> gives
> is that
> the 16C54 and the 16C84 use basicly the same instruction set.

The object code is different. The 16C54 has 12 bit instructions while the
16C84 has 14 bit. This difference shows up in register addressing, the
16C84 can address 128 registers directly while the 16C54 can only address 32.

The 16C84 also has 2 new instructions...

>Does that
> mean
>  that code
> written for the 54 will work in the 84 ??

For the most part. At the back of the 16C84 datasheet in one of the
appendixes there's a short list of caveats for conversion.

>         The reason I'm asking is I want to use some of the  applications
> on
> Microchip's web site for the 54 in my 84. Will it work ??

Again for the most part. The problem is that the subtle differences can
kill you. Be sure to read that appendix.

>         On a simular subject..can the 54 be programmed by the same
> programmer
> that I'm
> using for the 84 ?? ( It's DonTronics parallel port 7407 PNP type
> programmer ).

No for 2 reasons:

1) The 16C54 uses a 12 bit parallel data path. The 16C84 uses a serial
data path.
2) The EPROM for the 16C54 requires rather tight timing for programming
(100 microsecond pules to be specific) while the 16C84 with EEPROM is
self timing so the host doesn't have to really keep any timing at on while
programming it (other than to wait for it to finish).


>         I realize that it's an EPROM part and not an EEPROM so I would
> need a UV
> eraser to program it more than once.
>         Thanks !

That also true.

Personally I belive the 16C54 series is obsolete. Anything you want to do
with one of those parts is probably better served using either a 16C62X
or a 16C55X part.

For example at DigiKey (http://www.digikey.com) the erasable 16C620 is about
$1 more than the erasable 16C54. However is has over double the ram, the
typical 8 level stack (no subroutine problems), and is serially programmable
like the 16C84 (except the timing issues because of the EPROM)

So my advise is not to take a step backwards to the 16C5X series. While they
are great when you have simple tasks and need really inexpensive parts in
volume, their limitations both in architecture and programming makes them
unsuitable for hobby development. The 16C62X and 16C54X series are much
closer to the 16C84, so you'll have less problems changing over.

BAJ