From: Richard Atkinson (rga24_at_cantab.net)
Date: 2005-04-12 22:06:50
On Wed, 6 Apr 2005, [ISO-8859-2] Grósz Attila wrote:
> Watching at the disassembly, I think the bank selection
> register is at $df86 while the MV's TIA is accessed thru
> $df80-$df87. So both the speech chip and the bank selection
> are accessed via the TIA. These are the first impressions
> only though. Guess I have to take another look at the 6525
> data sheets as well...
I've had a go at hand-disassembling the first part of the Magic Voice
code, using information from the schematics. The code starts up in Ultimax
mode and there are pull-up resistors connected to the relevant lines on
the gate array and the C64 cartridge port so that they read high when the
6525 I/O ports are configured as inputs. I think the 6525 registers are
mirrored across the whole $DF00-$DFFF range, as A7 does not feature in the
logic. I put my commented disassembly up on the web:
http://www.atkinsoft.com/magic_voice_startup_code.txt
The code allows a few educated guesses at what some of the control signals
do. PB6 (connected to pin 9 of the gate array) seems to be used to select
between Magic Voice internal ROM (when high) and external cartridge ROM
connected to the pass-through connector (when low). PC6 looks like it
might be used as the C64 GAME# signal, via inversion in the gate array. I
think the GAME# function on the gate array should be an output not an
input. The unmarked signals (pins 7, 8 and 9) all appear to be inputs.
Will try disassembling the code copied to $C000-$C5FFF tonight.
Richard
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