Re: CIA Serial Data Register

From: Michael Huth <>
Date: Mon, 23 Feb 2015 12:23:15 +0100
Message-ID: <>

from my experience quite a few routines for hardware extensions used the 
CIA SDR register as temporary memory. (e.g. the IEEE488 interface 
published in 64er magazine) Since this register is by default unused it 
was a top candidate to be used.
While it is a quite convenient solution it gets problematic as soon as 
you start using the CIA for serial transfers. Then you have to start to 
find another memory location and patch all ROMs.


Am 2/23/2015 um 9:18 AM schrieb Baltissen, GJPAA (Ruud):
> Hallo allemaal,
> While disassembling SpeedDOS I noticed I encountered the use of SDR several times. My first reaction was: why? Then I realized that it maybe is used as a temporary data register. Never having used it myself, my question is: is that possible?
> If indeed so, it would answer quite some questions.
> With kind regards / met vriendelijke groet, Ruud Baltissen
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Received on 2015-02-23 13:00:05

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