Re: 2114 chips needed?

From: Ojala Pasi 'Albert' (
Date: 2001-01-09 09:43:16

> Three month ago I made a simple 32 KB-expansion for someone piggy-backing a
> 62256 (32*8KB SRAM) on top of the BASIC-ROM. A 74LS21 (dual 4-input AND)
> took care of ANDing the RAM and BLK-lines (not BLK5 !).
> there is interest, I'll make a SCH in GIF and check it with Pasi to see if
> this is what he had in mind.

Not quite, because for a cartridge you need to generate A13 and A14,
because they are not available in the cartridge port. My thought was
to use quad 2-input AND to generate the address bits and the chip
select for the RAM. Okay, I'll sketch the connection here..
            +---| \
            |   |  )-------------- A13ram
            | +-|_/
          H | |  _
/B1 --o o-+---+-| \
          H |   |  )----+--------- A14ram
/B2 --o o-+-----|_/     |   _
          H |    _      +--| \
/B3 --o o-+-+---| \        |  )--- /CSram
          H     |  )-------|_/
/B5 --o o-+-----|_/

VR/W ---o H
        o-+--- R/Wram
CR/W ---o

H is a pullup resistor, 100-470kOhm should work fine.
--o o-- is a place for a jumper block or a switch.
You should also add ~100nF capacitor between VDDram and GNDram.

You can disable all blocks separately and write-protect the whole
thing by removing jumpers.

If you use this style, it would be usable for both internal and
external expansion.

/His hands almost went to his ears in a strangely human gesture. Like a
 boy he looked, almost lost. God, that our immortal bodies could be such
 varied prisons for us, that our immortal faces should be such masks for
 our true souls./	-- Lestat in "The Vampire Lestat"
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