4. FDC Description (82078)
18
PERPENDICULAR RECORDING MODE
An added capability of the 82078 is the ability to interface directly to perpendicular
recording floppy drives that use the Toshiba format. Perpendicular recording differs from
the traditional longitudinal method by orienting the magnetic bits vertically. This scheme
then packs in more data bits for the same area.
The 82078 with perpendicular recording drives can, at a minimum, read standard 3½"
floppies as well as read and write perpendicular media. Some manufacturers offer
drives that can read and write standard and perpendicular media in a perpendicular
media drive. A single command puts the 82078 into perpendicular mode. All other
commands operate as they normally do. The perpendicular mode requires the 1 Mbps
data rate of the 82078. At this data rate, the FIFO eases the host interface bottleneck
due to the speed of data transfer to or from the disk, if utilized.
STATUS, DATA, AND CONTROL REGISTERS
The following topics discuss the status, data, and control registers of the 82078 FDC.
The base address range is supplied via the CS* pin. For PC-compatible designs, this is
3F0h to 3F7h. The following "82078 Register Summary" table summarizes addressing
for the status, data, and control registers.
82078 Register Summary
A2
A1
A0
Register
0
0
0
SRA - Status Register A
0
0
1
SRB - Status Register B
0
1
0
DOR - Digital Output Register
0
1
1
TDR - Reserved (Tape Drive Register)
1
0
0
MSR - Main Status Register
1
0
0
DSR - Datarate Select Register
1
0
1
FIFO - Data (FIFO)
1
1
0
Reserved (Not decoded)
1
1
1
DIR - Digital Input Register (Read)
1
1
1
CCR - Configuration Control Register (Write)
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