At 12:31 PM 4/13/2004, Eisermann, Phil [Ridg/CO] wrote:

>Cost and complexity are almost always interrelated. Cost is more
>than just component cost. I personally think that component cost
>only becomes relevant when you start talking about 10's or 100's of
>thousands of boards. I look at it in terms of design time e.g.
>engineering salary. In this case, DigiKey price for 100 16F872-ISO
>is $2.81. 100 12F629-ISO plus 74HC164 is 1.32. Difference is $1.49
>times 100 units = $149 dollars.

Another consideration to add to this discussion: power handling.  If you
need to drive large loads, it can be easier to use a SR with built-in high
current output stages.  I'm thinking of the TPIC6595 family but there are
others.

Once you have SPI code working, it becomes just another tool in the
arsenal.  Use it if it makes sense to do so, use a larger package PIC if not.

I use a LOT of 12c508 parts and using shift registers to provide the extra
I/O that I need seems completely natural.  But, then again, I've been using
shift registers since long before I even heard of PICs.

That said - for a one-off project being built from scratch (not able to use
an existing board design), I'd probably use one of the larger PICs *if* all
the I/O fits into one part.

dwayne


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Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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