Thanks for the information,

The catch that I was missing is the programming change and the lack of a
bootloader (I am using shane's on the 16F877).  Those are not too bad
though, and I am considering replacing the 16F877 in my current project with
one of the 18Fs

--BobG

-----Original Message-----
From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On
Behalf Of Byron A Jeff
Sent: Monday, July 29, 2002 12:47 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: What's the downside of the 18FXXX compared to 16F8XX

On Mon, Jul 29, 2002 at 12:06:47PM -0400, Robert E. Griffith wrote:
> I had been assuming that the newer, high-end 18FXXX PICs were more
expensive
> than the mid-range 16F8XX chips, but just noticed in the digikey catalog
> that they are about the same price.

That's the Microchip way. I certainly have to give it to them that they
consistently offer better products at a better value.

>
> So, what's the catch?  Is there any disadvantage to using say the 18F452
> over the 16F877?  Twice the program space appeals to me.  The peripherals
> seem roughly equivalent.

Well there's a few of things that will slow adoption a bit:

1) Parts availablity. Digikey is really just starting to get parts in
quantity.
This is another consistent Mchip trait. However once they start rolling off
the
fab... Watch out!

2) The programming algorithm is different. So while those of you with
picstarts
or Warp-13s can upgrade, us hobby folks with Tait style programmers will
have
to wait for (or program) the new programming algorithms. It's in the 10 top
of
my list of things to do for my version of picprg2.3

A good bootloader or two will significantly help in relieving this issue in
the
long term...

3) Somewhat incompatible instruction sets. There are both straight
translations (RLF to RLCF/RLNCF for example) and the more subtle
improvements
(multiple branch instructions, RLNCF/RRNCF, the multiply instructions, and
my
favorite: multiple FSRX/INDFX pairs!!) that will take a while to integrate
into the mindset.

My plan is a deliberate yet cautious migration up. Get a couple of parts,
update picprg2.3 (probably changing the name to 2.4 in the process), update
my
NPCI interpreter (and maybe actually get it finished and usable), and write
a
simple bootloader (if Wouter doesn't beat be to it... and he will so that's
why it's last on my list here...)

But there's no doubt the Mchip has done it again with the series. The speed,
the power, and the basic compatibility, along with a great price makes it
just as substantial an upgrade as the 16F87X/16F62X series were an upgrade
to
the 16F84.

I welcome the parts. I welcome the challenge.

BAJ

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