W83L517D_05 Datasheet, PDF (23/133 Pages) Winbond – LPC I/O for Notebook

W83L517D/W83L517D-F
6.1.4 Write Precompensation
The write precompensation logic is used to minimize bit shifts in the RDDATA stream from the disk
drive. Shifting of bits is a known phenomenon in magnetic media and is dependent on the disk media
and the floppy drive.
The FDC monitors the bit stream that is being sent to the drive. The data patterns that require
precompensation are well known. Depending upon the pattern, the bit is shifted either early or late
relative to the surrounding bits.
6.1.5 Perpendicular Recording Mode
The FDC is also capable of interfacing directly to perpendicular recording floppy drives. Perpendicular
recording differs from the traditional longitudinal method in that the magnetic bits are oriented
vertically. This scheme packs more data bits into the same area.
FDCs with perpendicular recording drives can read standard 3.5" floppy disks and can 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 FDC into perpendicular mode. All other commands operate as they
normally do. The perpendicular mode requires a 1 Mbps data rate for the FDC. At this data rate the
FIFO eases the host interface bottleneck due to the speed of data transfer to or from the disk.
6.1.6 FDC Core
The W83L517D FDC is capable of performing twenty commands. Each command is initiated by a
multi-byte transfer from the microprocessor. The result can also be a multi-byte transfer back to the
microprocessor. Each command consists of three phases: command, execution, and result.
Command
The microprocessor issues all required information to the controller to perform a specific operation.
Execution
The controller performs the specified operation.
Result
After the operation is completed, status information and other housekeeping information is provided to
the microprocessor.
6.1.7 FDC Commands
Command Symbol Descriptions:
C:
Cylinder number 0 - 256
D:
Data Pattern
DIR:
Step Direction
DIR = 0, step out
DIR = 1, step in
DS0:
Disk Drive Select 0
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Publication Release Date: May 23, 2005
Revision 1.0