Re: external ram expansion modules for 16k 264 series machines

From: Gerrit Heitsch <>
Date: Thu, 02 Aug 2012 21:20:34 +0200
Message-ID: <>
On 08/02/2012 09:08 PM, Imre Széll wrote:
> 2012/8/2 Gerrit Heitsch <
>     We also need to exclude I/O space ($FD00 to $FEFF?) and the TED
>     registers ($FF00 to $FF3F) from the RAM mapping. I assume that's
>     where the 13-input NAND on one of the boards comes in handy. Usually
>     TED does this decoding.
> You don't have to do that for yourself: the PLA handles the I/O space
> (from $fd00-$ff3f)

Yes, but I need to disable _CAS for the RAM on the card in that range. 
There is no signal from the PLA that tells me that the current address 
is in I/O space. That would mean some I/O-Chip (like the 1551 paddle) 
and the RAMs would be active at the same time without that decoder.

Also, since TED has access to all 16 address lines, it does its own 
decoding for its register space, no external signal available.


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Received on 2012-08-02 20:00:37

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