Another approach is to impliment a system like the basic stamp where you
run an interpreter on the chip with external memory holding the code. While
not an ideal solution it would allow you to expand memory at the cost of
speed and a couple of I/O pins.


At 02:16 PM 5/4/98 -0800, you wrote:
>Eric Slight <eslight@Matrox.COM> wrote:
>
>> > > if I buy a 16F84, I am stuck with only 1K of eeprom program memory,
>> > > is there a way to reroute the port for data/adress bus?
>> >
>> >     No.  If you want an external address/data bus, you'll need to
>> >     use one of the PIC17 family.
>>
>> You mean I'll have to buy a bigger romable code chip ?
>> or you mean there's a chip that you can hook up with the
>> pic that does the job, or what? :)
>>
>> I used to do ram expansion when needed with  68hc11 but the pic
>> doesn't work the same way and I don't know how to adress pass 3ff
>> with external memory, for example
>
>Eric:
>
>None of the 12- and 14-bit PICs (PIC12Cxxx, PIC14xxx, PIC16C5x,
>PIC16Cxx, etc.) support external program memory.
>
>The only PICs whose I/O pins can be configured as an external
>address/data bus (like the 68HC11 with which you're familiar) are
>the 16-bit PICs (PIC17C4x, etc.).
>
>If your code will not fit in your current PIC, you have two choices:
>
>    1.  Buy a PIC with more internal program memory than what you're
>        using now, or
>
>    2.  Replace your current PIC with a PIC17Cxx device, configure
>        it for either "microprocessor" or "extended microcontroller"
>        mode, then add all the external memory (and address-decoding
>        and latching logic) that you want.
>
>-Andy
>
>=== Andrew Warren - fastfwd@ix.netcom.com
>=== Fast Forward Engineering - Vista, California
>=== http://www.geocities.com/SiliconValley/2499 (personal)
>=== http://www.netcom.com/~fastfwd (business)
>
>
Larry G. Nelson Sr.
mailto:L.Nelson@ieee.org
http://www.ultranet.com/~nr