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PIC UPDATE 

Last month I wrote an article on PICs, Programmable Integrated
Circuits, and placed the article in several robot newsletters 
and also on USENET, an electronic news service. The response, 
especially from USENET, has been useful.  

First of all, we can forget about the Motorola 68L705. I
was told that after the current supply of parts is depleted, 
the 68L705 will no longer be available.  On the other hand, 
Microchip is strengthening its PIC line with an advancement 
over the PIC16C5x series called the PIC16C71 including these 
new additions:

 * Four 8-bit A/D Inputs 
 * Four Interrupt Sources 
 * Eight Level Hardware Stack 
 * Programmable On-board Pull-up Resistors 

The addition of Analog to Digital Converter Inputs makes 
the chip much more attractive. I can imagine several more 
applications using the analog capabilities. Too bad there is 
no Digital to Analog Converter. The external Interrupt 
allows an outside occurrence to trigger an action by the PIC 
as well as an internal timer Interrupt capability. The stack 
is eight deep getting rid of an annoying limitation on the 
16C5x series that are only two deep. And the programmable 
Pull-up simplyallows you to use fewer components in your
design -- a nice touch.  

Microchip also expanded the internal instruction word from 
12 bits to 14 bits. This cleaned up the instruction set. For
example, the Jump instruction can go anywhere in the 1K 
program memory without regard to what page it's on. Also the 
registers are all addressable without selecting register 
banks. These improvements create cleaner and faster code.

The new PIC requires a programmer upgrade from Parallax 
which cost $99 and is available now. My costs now are up to 
about $350 total. There are no Parallax ICE or emulators 
available yet. The PIC16C71 chips themselves are hard to get 
and right now and are only available on a sample basis. I 
suggest you call Microchip and get information on the office 
nearest you. 

Microchip Technology (602)963-7373 
Microchip (Sunnyvalle Office)(408)436-7950 
Trinity Technologies (Sunnyvalle) (408)733-9000 
Parallax,Inc (916)721-8217 

Brad Smallridge 
Phone (415)550-0588 
FAX (415)550-0411 
BBS (415)648-6427
EMAIL bsmall@holonet.net