Re: I/O Space is a Valuable Thing

From: Mike Naberezny (
Date: 1999-10-25 22:20:37

On Mon, 25 Oct 1999, [ISO-8859-1] Marko Mäkelä wrote:

> Wasn't this discussed a few months ago here?  Someone was going to compose
> a list of the addresses.  Maybe Richard Atkinson?  Anyway, the REU
> occupies $df00-$df0a or so, and there are mirrors at $df10,... (or maybe
> it was $df20; I don't have the REU at hand right now).  I modified one REU
> so that it can coexist with an Action Replay cart (which uses $de00-$deff
> for one 7-bit write-only register and $df00-$dfff for ROM or RAM).  The
> modification was a 3-position switch that would choose the REU registers
> to be read/write, write-only or completely disabled.  In write-only mode,
> detecting the REU reliably is impossible, and not many programs are likely
> to work in that mode.  But prlink does work. :-)

If it is mirrored throughout the entire address range maybe the $DE page
would be a better selection?  I don't want to mess with the REU.

I know from the past that the SL cartridge is not fully decoded either and
it is mirrored through the $DE page. It isn't that important to me, I can
fix it or make a better UART cartridge.  Does anything else use the $DE
area?  Where does the RAMLink fit into all of this?

> Maybe they are afraid of people making clones? :-)

Or they want to be the only ones making compatible hardware?

 - Mike Naberezny (

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