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 Message was sent through the cbm-hackers mailing list
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