Re: P500

From: Mike Naberezny <>
Date: Tue, 06 Nov 2012 13:41:48 -0800
Message-ID: <>
Hi Christian,

On 11/6/12 1:15 PM, Christian Dirks wrote:
> The screen scrolling seems very slow to me.
> Since I haven't seen a working P500 before, I don't know, if it is alwas that
> slow.
> The ROMs are -02's.

The screen slowness is normal.

You'll find a disassembly of the KERNAL ROM here:

The KERNAL calls special routines whenever it needs to write to the VIC-II 
registers (wrtvic), screen RAM (wrtvram), or color RAM (wrtcram).  As a 
result, the screen is quite slow.

These routines were to work around hardware instability.  I've never read an 
explanation of the specific issue.

Recently I have been experimenting with my P500.  I have a program that writes 
directly to the screen RAM and seems to work.  I've read of others doing the 
same with success.  It may be that not all P500 machines have the issue or 
that it only occurs under some conditions.


Mike Naberezny (

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Received on 2012-11-06 22:00:43

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