Re: GEOS cartridge

From: Gerrit Heitsch <>
Date: Tue, 18 Jun 2013 20:17:40 +0200
Message-ID: <>
On 06/18/2013 07:58 PM, wrote:
> Hallo allemaal,
> The good news: I replaced the unmarked ICs with marked ones and
> things worked out fine!

The schematics look a lot like the banking logic used in the 264 series. 
The C16 uses also uses a 74LS02 and a 74LS175 for this purpose. I wonder 
if the designer was inspired by it.

Your cartridge does not use the R/_W signal though, meaning that just 
reading the I/O-area will change the contents of the register.

> Also notice that, although you find 27C256s in the schematic, pin 1
> can be controlled as well. So one could use 27512s as well. IMHO a
> design usable for other purposes as well.

If I was to use the circuit for something else, I'd change the logic so 
that only writing to the I/O-area would change the banking register. 
Unless I'm completly mistaken, you should be able to add R/_W to the mix 
with the 2 unused LS02 gates.


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Received on 2013-06-18 19:01:19

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