I have been analyzing the 5710 chip in the C128D drive and the effect it
has on the memory configuration. The memory maps below show some
interesting differences.
The 5710 replaces the WD1770 and the 6526 and some other logic in the 1571
drive.
The 2K RAM appears at 0000-0FFF in both drives, but also appears at
6000-7FFF in the C128D.
The FDC in the 5710 has 6 registers at 2000-2005, whereas the WD1770 has
only 4. What are the other 2 for??
The 6526 replacement is even stranger. In the 1571, the 6526 is used only
for it's serial port. The equivalent 16 locations in the 5710 read
fixed values. Since these values are not all FF, it would appear that
this was done intentionally, but why? The real 6526 replacement occupies
the next 8 bytes which can be read and written. I have not worked out
what they actually do.
1571 C128D 1571
0000-07FF RAM 0000-07FF RAM
0800-0FFF RAM shadow 0800-0FFF RAM shadow
1000-17FF Not Connected 1000-17FF Not Connected
1800-180F 6522 VIA1 1800-180F 6522 VIA1
1810-1BFF VIA1 shadows 1810-1BFF VIA1 shadows
1C00-1COF 6522 VIA2 1C00-1COF 6522 VIA2
1C10-1FFF VIA2 shadows 1C10-1FFF VIA2 shadows
2000-2003 WD1770 FDC 2000-2005 5710 FDC
2004-3FFF WD1770 shadows 2006-2007 FF FF
... 2008-201F Not Connected
... 2010-2FFF 2000-201F shadows
... 3000-3FFF Not Connected
4000-400F 6526 4000-4007 FF FF FF FF FF FF FF FF
4010-7FFF 6526 shadows 4008-400F FF FF FF FF 00 F7 BF FF
... 4010-4017 5710 6526
... 4018-401F 6526 shadow
... 4020-43FF 4010-401F shadows
... 4400-440F 4000-400F shadow
... 4410-441F Not Connected
... 4420-47FF 4410-441F shadows
... 4800-4FFF 4000-47FF shadow
... 5000-5FFF Not Connected
... 6000-7FFF RAM shadows
8000-FFFF ROM 8000-FFFF ROM
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