ACT apricot - Fdcdetail; General

FLOPPY DISK INTERFACE
An optional feature of each of the five commands is to
automatically verify the track position of the head, by
comparing
the track number stored within an internal
register (Track Register) with the track number contained in
the ID fields on the disk. The verification operation also
checks
the ID field for errors utilising the ID field CRC
bytes. Failure to detect the same track number or incorrect
CRC detection, sets error status bits within the Status
Register. Since this feature involves reading the disk ID
field,
the head has to be loaded prior to the command.
The signals supplied by the FDC to the disk drive, to
position the read/write head are the STEP and DIRC
(direction) outputs. A step pulse with a duration of 2 fJ-S is
issued
to the drive every time the FDC wants to move the
head by one track location. The FDC determines the
direction of movement implied by the command and sets
the state of the direction output accordingly. (Logic high to
move the head away from Track 0, logic low to move the
head towards Track 0).
FDCDETAIL
General
The FDC can be divided from a descriptive point of view
into three areas of circuitry, a processor interface, a disk
drive controller, and a series of registers.
The processor interface handles the transfer of data,
commands and status, between the internal registers and
the system processors, and also generates the interrupt and
DMA request signals.
The disk drive controller responds to commands from the
CPU, providing the neccessary circuitry, and input and
output lines for:
(a) Controlling the positioning of the drive read/write
head.
(b) Transferring data to and from the disks.
(c) Monitoring the disk drive status.