Hard Sector Floppy Emulator

Hard Sector Floppy Emulator
C. Elmquist, N0JCF July 2009

HSFE is a small circuit using an ATMEL micro-controller that sits between a vintage computer's hard sector floppy controller and one or two 3.5" 1.44MB floppy drives. The circuit then emulates hard sectored floppy media such that the host controller thinks it is talking to legacy hard sectored 5.25" floppies.

HSFE has the following specifications and limitations:
· emulates 10-hole hard sectored floppies only
· emulates one or two drives simultaneously
· uses a standard PC floppy cable with "twist" between HSFE and 3.5" drives
· uses 1.44MB 3.5" media with the high-density hole covered with black tape
· tested with Heath H89 H-88-1 controller
· tested with HDOS 2
· tested with CP/M 2.2.X03
· tested with BIOS-80 extension for CP/M resulting in 100K, 200K and 400K storage on 3.5" media with H-88-1 controller.
· Each emulated drive can be connected to any of the four drive selects SY0, SY1, DRIVE1 or DS0 (DS0 unsupported on H-88-1).

You must use a 3.5" floppy drive that is capable of 720K low-density format on a PC. Some cheap 3.5" drives today omit the density sensor and force the drive into 1.44MB mode all the time. The Samsung SFD-321B is an example of one of these drives. These will not work with the HSFE and your H8 or H89 hard sector controller because they are unable to operate at the 250Kbps data rate that those controllers require.

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