Summer is finally coming :) And school's ending tomorrow.
It means that I'll have a lot of time to work with PIC.

So, I'm going to make a PLD with PIC16F84 being it's heart.

To overcome IO's, I've came up to something like this:

     output enabled ------------o---------o------- - -
                                |         |
PIC           latch --------o---+--o------+--o---- - -
RA0:3                       |   |  |      |  |
                            |  ------    ------
               data ----o---+--|    |----|    |--- - -
                        |   |  |4094|    |4094|
                     R | |  |  |    |    |    |
                       | |  |  ------    ------
                        T   |    |         |
              clock ----+---+----o---------o------ - -
                        |   |    |         |
                        |   |  ------    ------
                        |   |  |    |    |    |
                        L---+--|4014|----|4014|--- - -
                            |  |    |    |    |
                            |  ------    ------
                            |    |         |
                            L----o---------o------ - -

This gives me as many IO's as I need. All inputs would be opto
isolated, and outputs done with relays. Well, not now, but when
I get back to school and won't be spending my money :) 24 I's and
16 O's sounds like a start ;)

But, the more there are IO's, the more there should be memory
for the program. Those PLD macros (from SiStudio ftp ) eat about
five bytes of memory per instruction, so external eeprom will be
needed in some phase (though you don't run far with 68 bytes
of ram :) .

So, any ideas (and perhaps experience) how to use parallel eeproms
with PIC? I can use maximum of ten PIC pins for eeprom, and all
writes (loading _tokens_) and reads (execute _tokens_) would be
sequential. There should be a way to reset the address in the end
of the program. A 12 bit binary counter with clock & reset for
address? Are there any 4 bit eeproms?

Please note, that no serial eeprom can be fast enough. Not with
4 MHz. Not even with 20 MHz.


Kimmo

ps. I've studied 1 year of automation technology with people under 18.
This kind of stuff isn't taught there. In polytechnic perhaps...

As The Queen said to Alice,
you have to run to even stay where you are...