Dudes:

Here's a message that I wrote and sent right around the 20th.  If it
made it through the list-server "glitch", please ignore it this time:

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From: fastfwd@ix.netcom.com (Andrew Warren)
Subject: Re: AD/DA's and memory
To:  pic microcontroller discussion list
<PICLIST%MITVMA.BITNET@uga.cc.uga.edu>

Tracy Reed (treed@ucssun1.sdsu.edu) wrote:

>Without external address/data buses, where will I store the data
>recorded in flight?

        Use a serial EEPROM or two (or eight).  Microchip makes a
        24C65 that's perfect for your application.  Eight of them
        will hold 64K bytes of data, and they'll only require two
        PIC I/O pins total.


>Would the external memory really complicate things that much?

        Yes.  To build a PIC17C42-based circuit with an external bus,
        you'd need an EPROM, a RAM, a parallel EEPROM or two, a few
        8-bit latches, a bunch of address-decoding chips, a multi-layer
        PCB designed by a good layout person, a really good scope, a
        logic analyzer, and enough money to go through a few board revs.

        If you were really on the ball, you could replace the latches,
        ROM, RAM, and address-decoding chips with one of those WSI
        chips, but then you'd have to learn to use their compiler
        (almost as much work as just building the circuit out of
        discrete components).

>Why would I want an OTP? I thought EEPROM would be just fine.

        You'd want OTP (as opposed to masked ROM) for production.  For
        development, you'd want the erasable equivalent (EPROM).  EEPROM
        program memory is available only on the 16C84, which has no A/Ds
        and much less memory than the 16C74.

>I clearly need to read some books and learn a bit more before I will
>really be able to choose what micro is best for the job.

        Yeah... I'm sure you'll have a much better idea of what you're
        doing after you get and read the Data Book and Embedded Control
        Handbook.

------------------------------------------------------------------------

-Andy



--
Andrew Warren - fastfwd@ix.netcom.com
Fast Forward Engineering, Vista, California