Difference between revisions of "Four floppy drives with Amstrad disc interface"
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2 drives (A1 and A2) are in the collection for drive A. A switch chooses which A1 or A2 is drive A. | 2 drives (A1 and A2) are in the collection for drive A. A switch chooses which A1 or A2 is drive A. | ||
2 drives (B1 and B2) are in the collection for drive B. A switch chooses which B1 or B2 is drive B. | 2 drives (B1 and B2) are in the collection for drive B. A switch chooses which B1 or B2 is drive B. | ||
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Latest revision as of 03:56, 1 September 2014
Four floppy drives with Amstrad disc interface
The Amstrad disc interface (DDI-1 or the disc hardware within CPC664, CPC6128 and 6128+) supports a maximum of 2 drives, although the NEC765 used within the interface supports up to 4 drives.
NOTE: The Vortex disc interface, the version which contains the NEC765 can access up to 4 drives directly.
Four drives hardware modification
The NEC765 floppy disc controller used by Amstrad can support up to 4 drives. However, in the Amstrad disc interface, only the US0 output is connected. This then decodes into two drive selects (/DRIVE SELECT 0 and /DRIVE SELECT 1).
The CPC6128 uses a 74LS38 (Quad 2-input NAND) to generate the select for drive 1, the select for drive 0 is generated from this using VCC, resistor and KTC1815.
With a hardware modification, internal in the CPC664, CPC6128 or 6128+, or internal to the DDI-1, the US1 output can also be connected, and now four drives can be accessed using the NEC765 directly.
To do this a 2-to-4 decoder should be used instead. (i.e. 74LS139)
Note that most Amstrad software, including AMSDOS supports only 2 drives. So to use the 4 drives you need to access the NEC765 directly.
FutureOS supports this hardware modification and can use the 4 floppy drives. (As a side note, FutureOS supports 8 floppy drives, but the other 4 are provided by adding a Vortex Disc Interface in addition to an Amstrad Disc interface).
Alternatives
It is possible to use 4 drives without any internal modifications. The NEC765 will still see 2 drives and this method is compatible with all existing software. Using switches you can choose 1 drive out of a collection of drives to act as A, and with a second switch choose 1 drive out of another collection to act as B.
e.g. 2 drives (A1 and A2) are in the collection for drive A. A switch chooses which A1 or A2 is drive A. 2 drives (B1 and B2) are in the collection for drive B. A switch chooses which B1 or B2 is drive B.
