W83877 Winbond Electronics Corp America, W83877 Datasheet - Page 20

• Manufacturer Part Number: W83877
• Description: Winbond I/O
• Manufacturer: Winbond Electronics Corp America

W83877F
into byte mode (FIFO disabled) and is programmed to do a read. With the FIFO enabled the above
operation is performed by using the new VERIFY command. No DMA operation is needed. ¡@
2.1.3 Data Separator
The function of the data separator is to lock onto the incoming serial read data. When a lock is
achieved the serial front end logic of the chip is provided with a clock which is synchronized to the
read data. The synchronized clock, called the Data Window, is used to internally sample the serial
data portion of the bit cell, and the alternate state samples the clock portion. Serial to parallel
conversion logic separates the read data into clock and data bytes.
The Digital Data Separator (DDS) has three parts: control logic, error adjustment, and speed tracking.
The DDS circuit cycles once every 12 clock cycles ideally. Any data pulse input will be synchronized
and then adjusted by immediate error adjustment. The control logic will generate RDD and RWD for
every pulse input. During any cycle where no data pulse is present, the DDS cycles are based on
speed. A digital integrator is used to keep track of the speed changes in the input data stream.
2.1.4 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.
2.1.5 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.
2.1.6 FDC Core
The W83877F 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.
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