PIC17C756 replacement

Started by mmk_tsm February 6, 2009
Hello,
My comapany (industrial controls) has been using a PIC17C756 as
the sole microcontroller on all our smaller control boards for a long
number of years. It has proven to be fantastically reliable. It is a
68 pin PLCC device, and so has a large no. of i/o pins. But it is old,
expensive, and OTP.
It is time to upgrade to something more modern, flash based, in
system programmable, but hopefully something in a similar footprint to
minimise re-design.
Can anyone recommend a good device, one of the most important
criteria is longevity, i.e. something that is now popular and so
should still be around in 10years time.
And can anyone point me to a microchip device cross-reference
table please.
TiA,
M.

----- Original Message -----
From: "mmk_tsm"
To:
Sent: Thursday, January 01, 2009 4:44 PM
Subject: [piclist] PIC17C756 replacement
> Can anyone recommend a good device, one of the most important
> criteria is longevity, i.e. something that is now popular and so
> should still be around in 10years time.

It is hard to call what Microchip's marketing strategies are going to be
next week, let alone next decade, but I suspect your choice is going to be
driven to some degree by your volume.

Some of the newer 16 bit parts are likely to outlast the less capable parts
(IMO), but they are also going to be more expensive. However, I suspect
some killer parts are going to be less expensive than your 17C, so you're
going to be making some guess as to the risk of a part going away against
some price difference. If you are shipping a few hundred units then the
redevelopment risk will probably drive your decision. If you are shipping a
few million, then a few cents a part can be a big deal.

These days, however, there are plenty of parts with lots of legs to choose
from. Perhaps more interesting, parts with huge amounts of flash and ram
and very elaborate peripherals can be very inexpensive.

> And can anyone point me to a microchip device cross-reference
> table please.

I haven't seen a good cross-reference, but the product selector ought to
help. The 17C was an odd bird, so almost anything is going to result in
code changes. One thing to keep in mind, many of the 24F parts have
assignable I/O pins, so those parts may help you cut down on board redesign.

A quick look at the product selector shows no 68 pin parts, but there are
178 parts in the 8-bit "64, 80, 100 pin" group,
http://www.microchip.com/ParamChartSearch/chart.aspx?branchID36&mid〈=en&pageIdt
and the same number in the 16 bit family,
http://www.microchip.com/ParamChartSearch/chart.aspx?branchID73&mid〈=en&pageIdu
so there is no lack of large pin count devices. Although I would suggest
you seriously consider the 16 bit parts if you are looking for longevity,
except for the dsPIC30 series, which offers features you don't need, all of
the 16 bit parts are 3.3 volt parts, which may be an issue since presumably
your 17C was a 5 volt design.

Also keep in mind that when a part is on the way out, it seems like the
price goes up, so I would avoid a part that is expensive for what you get.

--McD

----- Original Message -----
From: "mmk_tsm"
To:
Sent: Thursday, January 01, 2009 4:44 PM
Subject: [piclist] PIC17C756 replacement
One thing I failed to mention -- none of the PIC24 parts have EEPROM, but
they all have writable flash which, depending on your application, could
serve as a substitute. The big difference is that while you are writing the
flash you are not executing instructions. If your application is fairly
leisurely, that might work, but if you need to continue working while the
write is in progress, that could be an issue.

Also note that the 24F parts are only 16 MHz, while the 24H are faster, up
to 40. But obviously, what you gain in clock ticks you pay for in power
consumption.

--McD