Fujitsu MHT2020AT, Product Manual

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4.6 Read/write Circuit
C141-E192-01EN 4-9
4.5.3 Command processing during self-calibration
This enables the host to execute the command without waiting for a long time,
even when the disk drive is performing self-calibration. The command execution
wait time is about maximum 72 ms.
When the error rate of data reading, writing, or seeking becomes lower than the
specified value, self-calibration is performed to maintain disk drive stability.
If the disk drive receives a command execution request from the host while
performing self-calibration, it stops the self-calibration and starts to execute the
command. In other words, if a disk read or write service is necessary, the disk
drive positions the head to the track requested by the host, reads or writes data,
and then restarts calibration after 10 seconds.
If the error rate recovers to a value exceeding the specified value, self-calibration
is not performed.
4.6 Read/write Circuit
The read/write circuit consists of the read/write preamplifier (PreAMP), the write
circuit, the read circuit, and the time base generator in the read channel (RDC).
Figure 4.4 is a block diagram of the read/write circuit.
4.6.1 Read/write preamplifier (PreAMP)
PreAMP equips a read preamplifier and a write current switch, that sets the bias
current to the MR device and the current in writing. Each channel is connected to
each data head, and PreAMP switches channel by serial I/O. In the event of any
abnormalities, including a head short-circuit or head open circuit, the write unsafe
signal is generated so that abnormal write does not occur.
4.6.2 Write circuit
The write data is output from the hard disk controller (HDC) with the NRZ data
format, and sent to the encoder circuit in the RDC. The NRZ write data is
converted from 32-bit data to 34-bit data by the encoder circuit then sent to the
HDIC, and the data is written onto the media.
(1) 32/34 RLL MEEPRML
This device converts data using the 32/34 RLL (Run Length Limited) algorithm.
(2) Write precompensation
Write precompensation compensates, during a write process, for write non-
linearity generated at reading.