Write Circuit - Fujitsu MAB3091FC Series Maintenance Manual

5.6.2

Write circuit

The write data is converted into the NRZ data (WDT), and is sent, together with the Write
clock (WCLK) signal, to the write circuit. The NRZ data is converted into 8/9 RLL code by
the encoder circuit, and is written to the disk.
(1) 8/9 RLL encoder
This disk drive uses the 8/9 RLL recording method. The NRZ data sent from the SCSI controller is
converted into pseudorandom data by the scrambler circuit. The 8/9 RLL encoder then converts 8-
bit NRZ data into a 9-bit 8/9 RLL code. This conversion is represented by the logical expressions
below.
In an 8/9 RLL code, when the 9-bit code string is separated to the even string and odd string,
up to four 0's are inserted between two "1" bits.
When the data bit period is t, the minimum code bit period of any input data is from 8t/9 to
32t/9. Figure 5.5 shows a conversion example for 8/9 RLL code.
Assume that:
NRZ data string
8/9 RLL code string =
In this case, the relationship is as follows:
Y1=X1+R1+S1×X4
Y2=M1×X2+R1+S1
Y3=X3+R1+S1×X4
Y4=M1×X4+N1×X2+R1×X4+S1×
(X5+S2)
where
M=(X1+X2+X3)×(X4+X5)×(X6+X7+X8)+X2×X7
M1=M+(X1+X3)×X4
N1=M×(X1+X3)×X4
R1=M×(X1+X3)×X2
S1=(X1+X2+X3)
5 - 8
(X1, X2, X3, X4, X5, X6, X7, X8)
(Y1, Y2, Y3, Y4, Y5, Y6, Y7, Y8, Y9)
Y5=M× (X1×X2×X3×X4×X5×X6×X7×X8)
Y6=M2×X5+N2×X7+R2×X5+S2× (X4+S1)
Y7=X6+R2+S2×X5
Y8=M2×X7+R2+S2
Y9=X8+R2+S2×X5
M2=M+(X8+X6)×X5
N2=M×(X8+X6)×X5
R2=M×(X8+X6)×X7
S2=(X8+X7+X6)
C141-F028-01EN