Re: UltiMax schematics

From: donni (
Date: 2008-11-27 17:47:34

Why can't you believe that the CIA chip select has to run tru the cartridge 
Like I said, I reversed engineerd this schematic with a MAX machine in front 
of me.
Why commodore did it that way beats me, I can't think of an application that 
would benefit from a disabled CIA.
The circuit on the R/W line of the PLA looks like a buffer with a RC filter, 
not sure why it is needed.
Maybe to filter out some of the noise on the R/W line?


----- Original Message ----- 
From: <>
To: <>
Sent: Thursday, November 27, 2008 12:40 PM
Subject: UltiMax schematics

> Hallo allemaal,
> I'm busy with the SCH and I have a question, but first some facts: the
> 6703 PLA outputs a signal at pin 23 called CIA PLA. The expansion port
> has has two signals called CIA and CIA PLA. The 6526 has a signal
> labeled CIA connected to input CS. And that are all the signals related
> to CIA I could find. According this SCH the 6526 can only be used if an
> cartridge is inserted that connects CIA and CIA PLA, something I hardly
> believe. Can someone shed some light on the case, please?
> Then a question out of curiousity: what is the idea behing using
> transistor Q8 in the R/W line towards the 6703 PLA?
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