This is a replica of the original Acorn Floppy Disk Controller for the Atom Computer, it is usually fitted inside an enclosure with a pair of 5.25" floppy disk drives, see the Atom Disk Pack. However the board can be fitted internally to the Atom using my Atom Riser Card.
The board uses an Intel 8271 controller, the original Acorn design was intended for use with 5.25" floppy drives and was not reliable with 3.5" drives. I have made a small design change which allows it to be used with 3.5" floppy drives without modification. It will also work with GOTEKs.
The board incorporates two 64-way DIN connectors, PL2 connects to the Atom bus via PL6 (when fitted externally) and PL7 (when fitted internally). The second connector, PL3, is for the connection of an external memory expansion card (I've never seen one of these or any info about it ?).
PL4 provides a standard 34-way ribbon connection to one or two drives.
LK1 allows selection of either 5.25" drives operation only or additional 3.5" drive compatibility.
Power can be provided from the Atom bus (via PL6/7-PL2) by fitting LK2. Alternatively power can be provided via PL1, this is normally used when in an external enclosure, LK2 is then not fitted.
The board adds an additional 3K of RAM to the Atom, 2K at $2000 which is mostly used by DOS and a further 1K at $3C00. The board also carries a socket for a 2532 4K EPROM containing Atom DOS (at $E000).
The following pictures show the board installed in an Atom using the Atom Riser Card. I have fitted a piece of 1mm thick foam sheet on the underside to protect the board from shorting on the main Atom PCB. Its a tight fit but just about works.
Schematic
Bill Of Materials
Blank PCB
