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C141-E056-01EN 4 - 9
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)
One PreAMP is mounted on the FPC. The PreAMP consists of an 6-channel read preamplifier
and a write current switch and senses a write error. Each channel is connected to each data
head. The head IC switches the heads by the serial port (SDEN, SCLK, SDATA). The IC
generates a write error sense signal (WUS) when a write error occurs due to head short-circuit
or head disconnection.
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 with synchronizing with the write clock. The NRZ
write data is converted from 8-bit data to 9-bit data by the encoder circuit then sent to the
PreAMP, and the data is written onto the media.
(1) 8/9 GCR
The disk drive converts data using the 8/9 (0, 4, 4) group coded recording (GCR) algorithm.
This code format is 0 to 4 code bit "0"s are placed between "1"s.
(2) Write precompensation
Write precompensation compensates, during a write process, for write non-linearity generated
at reading. Table 4.2 shows the write precompensation algorithm.
Table 4.2 Write precompensation algorithm
Bit Bit Bit Compensation
n – 1 n n + 1 Bit n
0 1 1 None
1 1 0 Late
1 1 0 Late
Late: Bit is time shifted (delayed) from its nominal time position towards the
bit n+1 time position.