Re: GEOS cartridge

From: Gerrit Heitsch <*gerrit_at_laosinh.s.bawue.de*> Date: Tue, 18 Jun 2013 20:17:40 +0200 Message-ID: <51C0A444.4060803@laosinh.s.bawue.de> · gerrit_at_laosinh.s.bawue.de

On 06/18/2013 07:58 PM, Ruud@Baltissen.org 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.

  Gerrit

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