Hi,
In Sony machines and in NMS8245, some wd2793 registers (track, sector) are
write only. In first version of fastcopy I mantained track number and sector
number by just looking at the registers. This version did not work on Sony or
NMS8245. Later, I corrected by maintaining track number and sector number in
variables in the program and write them to the registers whenever needed.
For the rest: 7FFD is a little bit more subtile:
bit 1,0 : drive number
bit 7: motor on/off (and not simply 'in use' led)
Following bit table is applicable for the two drive number bits:
B1 B0
0 0 : drive A selected
1 0 : drive A selected
0 1 : drive B selected
1 1 : no drive selected
And 7FFF is also wired (at least in Philips, I'm not sure anymore about Sony):
bit 6: !INTRQ
bit 7: !DTRQ
I do not see a direct practicle usage for reading out the INTRQ and DTRQ
signals of the wd2793 controller. But applications may exists that do rely on
them so a perfect emulation should emulate these bits as well. But I think
that in reality 99.999% of MSX software will work if you do not emulate them.
Kind regards,
Alex Wulms
]
] I'm working in disk emulation via the wd2793 in mess. This will have far more
] authentic emulation. First of all I'm working on emulating the Philips diskrom,
] I've found the following:
]
] Write:
]
] 7FF8: wd2793 command register
] 7FF9: wd2793 track register
] 7FFA: wd2793 sector register
] 7FFB: wd2793 data register
] 7FFC: side select. bit 0 : 0 => side 0, 1 => side 1
] 7FFD: drive select. bit 1-0 => drive. bit 7 => "in use" led
] (led on if bit is set and right drive in bit 1-0).
] 7FFE: nothing
] 7FFF: nothing
]
] Read:
]
] 7FF8: wd2793 status register
] 7FF9: wd2793 track register
] 7FFA: wd2793 sector register
] 7FFB: wd2793 data register
] 7FFC: bits 7-1 set, bit 0 is last value written
] 7FFD: bits 6-2 set, bit 7,1,0 is last value written
] 7FFE: unused (0xff)
] 7FFF: bits 5-0 set, bit 7 set if data request, bit 6 reset if interrupt request
]
]
] Can someone verify the correctness of this? Also does anyone know if the
] Sony machines use the same layout?
]
]
] Cheers,
]
] Sean
]
]
] --
] For info, see http://www.stack.nl/~wynke/MSX/listinfo.html
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