ACT apricot - Disk Formatting

FLOPPY DISK INTERFACE
bus. The FDC then searches the disk for the source of the
data (correct side, track and sector, with correct ID CRC
bytes).
Whenthe required location is found, the FDC begins
the process of reading data from the disk.
The MFM encoded data is decoded, assembled into
parallel data bytes, and transferred into the Data Register.
Every
time a parallel data byte is transferred into the Data
Register, the FDC signifies to the lOP that a data byte is
available by
issuing a DMA request, via the DRQ output.
Every
time the lOP reads the assembled data byte, the
FDC resets the DRQ output.
This process continues until the whole of the read
operation is
completed (reading the data from either a single
sector
or from multiple sectors within a track). The FDC
then generates an interrupt request on the INTRQ output,
which informs the lOP to terminate the DMA transfer
routine and also indicates to the CPU, the end of the
command cycle. Any errors produced during the transfer
can
then be checked by the CPU analysing the FDC status
register.
Disk Formatting
Disk formatting is a similar process to disk write
operations but involves transferring both data and gap
information /unintelligent information used to separate
areas of
data on the disk, see Figure 2) onto the disk, and is
executed
on a track-by-track basis. The process is initiated
by the CPU issuing a Write Track command to the FDC, via
the peripherals data bus. The FDC responds by signifying to
the lOP that a byte is required by issuing a DMA request,
via
the DRQ output.
The lOP then writes the first gap byte into the holding
register
/Data Register) within the FDC. The FDC resets the
DRQ output and then waits for the Index Pulse (the marker
for the start of a track) to be detected.