Data processing apparatus

There is provided a data processing apparatus for encoding or decoding binary data such as a magnetic disk or an optical disk in which a binary data sequence is converted to a binary code sequence which is suitable for a data processes. This data processing apparatus comprises: a code converter for converting the m-bit data in the binary data sequence to the n-bit code corresponding thereto; output means for outputting the n-bit code sequence corresponding to the binary data sequence; and DC-freeing means for restricting the DC component of the code sequence which is outputted from the output means. The code converter has a ROM table to store the data for code conversion and a register for converting the m-bit serial data to the parallel data and can be easily constituted by a programmable array logic.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a data processing apparatus for coding or 
decoding or the like of binary data in which binary data sequence is 
converted to a binary code sequence which is suitable for data processes 
in an electronic apparatus such as a magnetic disk, optical disk, data 
transmitting apparatus, or the like. 
2. Description of the Prior Art 
Hitherto, in electronic apparatuses such as a magnetic disk, optical disk, 
data transmitting apparatus, or the like, it is necessary to record or 
transmit a great amount of information. For instance, in recording, it is 
inevitable to improve recording density upon the recording of binary data 
on a recording medium. 
On one hand, in transmitting, it is inevitable to improve transmission 
speed. In addition, various kinds of coding and decoding systems have been 
proposed. 
FIG. 1 is a diagram for explaining one example of conventional coding 
systems. FIG. 1(a) shows an example of a bit pattern of an original binary 
data sequence, in which numerals 0 and 1 denote bit logics "0" and "1" and 
T.sub.0 represents a bit interval. FIGS. 1(b) and 1(d) respectively show 
one example of conventional coding systems, in which the system of FIG. 
1(b) is called an MFM system (Modified FM system) and the system of FIG. 
1(d) is called a 3PM system (3 Position Modulation system). When the 
recording technology is described, as an example of the apparatuses to 
which the foregoing respective systems are applied, the MFM system is used 
in the magnetic disk apparatuses (models 3330, 3340, 3350, etc.) made by 
IBM Corporation and the 3PM system is used in the magnetic disk apparatus 
(Model 8434) made by UNIVAC Corporation. For the algorithm of each system, 
in case of the MFM system, the original data "1" and "0" are converted to 
"01" and "X0" in correspondence thereto. However, in the coded sequence 
after conversion, " X" becomes a plurality of logics (1.fwdarw.0, 
0.fwdarw.1) of the code bit immediately before X. On one hand, for the 
algorithm of the 3PM system, the original data is separated on a 3-bit 
unit basis and is converted to 6-bit codes as shown in Table 1. 
TABLE 1 
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Coding Algorithm of the 3PM System 
Original Conversion 
data code Condition 
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000 000010 
001 000100 
010 010000 When a pattern "101" is 
011 010010 generated in the code 
100 001000 sequence after conver- 
101 100000 sion, it is converted 
110 100010 to "010". 
111 100100 
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For the coded sequence converted by each of the coding systems, a recording 
current is produced so as to become a signal such that the magnetization 
inversion occurs for a bit of "1" and the magnetization inversion does not 
occur for a bit of "0" and is recorded on the foregoing recording medium. 
FIGS. 1(c) and 1(e) show waveforms (NRZI signal) of the recording currents 
of the code systems which were coded by the MFM system of FIG. 1(b) and by 
the 3PM system of FIG. 1(d). 
Generally, in the recording on the magnetic medium, 
(a) When the magnetization inversion interval (recording wavelength) 
becomes short, the magnetic transitions due to the magnetization 
inversions before and after this interval are mutually interfered, thereby 
producing a cause for occurrence of errors upon decoding of the 
reproduction signal. 
(b) Even in the case where a demodulation phase margin (TW) (which will be 
explained later) upon reproduction to the recording wavelength is small, 
the same errors as mentioned above could be easily caused. 
(c) When the recording wavelength is larger as compared with the period of 
the clock signal for demodulation which is produced from the reproduction 
signal, the above-mentioned clock cannot be produced accurately from the 
reproduction signal, so that the same errors as mentioned above could be 
easily caused. 
(d) When a ratio between the maximum value and the minimum value of the 
magnetization inversion interval becomes large, the waveform interference 
(called the pattern peak shift) of the reproduction signal increases, so 
that the same errors as mentioned above could be easily caused. 
Thus, in the general coding systems, as the parameters indicative of the 
capabilities including the foregoing four items (a) to (d), the following 
variables are given. It is now assumed that in a certain coding system, 
the m-bit binary data sequence is converted to the binary code sequence of 
n (n.gtoreq.m) bits, and the minimum value of the number of codes of "0" 
between the code "1" selected arbitrarily from among the code sequence 
after conversion and the next code "1" is d and its maximum value is k. 
From this assumption, we have 
##EQU1## 
where, T.sub.0 is one original data period. 
Therefore, from the above description, it is desirable that the values of 
equations (1) and (4) are larger (from the explanations in the foregoing 
items (a) and (b)). On one hand, it is preferable that the value of the 
demodulation clock period in equation (3), the ratio of the maximum 
magnetization inversion interval (equation (5)) mentioned below and the 
ratio between the maximum and minimum magnetization inversion intervals 
(equation (6)) mentioned below are smaller. 
##EQU2## 
The above-mentioned parameters are shown in Table 2 with regard to the 
foregoing MFM and 3PM coding systems. 
TABLE 2 
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Parameters of Each Coding System 
Parameter 
Coding T.sub.max / 
T.sub.max / 
system T.sub.min 
T.sub.W C.sub.LK 
T.sub.min 
T.sub.max 
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MFM system 
T.sub.0 0.5 T.sub.0 
4 2 2T 
3PM system 
1.5 T.sub.0 
0.5 T.sub.0 
12 4 6T 
FM system 0.5 T.sub.0 
0.5 T.sub.0 
2 2 T 
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In addition, as described above, in the general coding systems, original 
data is converted to the n-bit code for every m bits and is expressed as 
(m, n, d, k) codes in which the run length of "0" of the code after 
conversion is restricted to a value which is not smaller than d and not 
larger than k. However, the handling number m (m.ltoreq.n) of this data 
bit affects the hardware of the apparatus. In this case, it is generally 
desirable that a value of m is small. When the foregoing coding systems 
are expressed by the (m, n, d, k) parameters, they will become (1, 2, 0, 
1) in case of the FM coding system; (1, 2, 1, 3) in case of the MFM coding 
system; and (3, 6, 2, 11) in case of the 3PM coding system. On one hand, 
what is called a DC free code of which a variation in DC component of the 
coded signal is suppressed is also generally desired. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a data processing 
apparatus in which: the T.sub.min is made as large as possible so as to 
avoid including the high frequency component and to reduce being subjected 
to the influence of the band restriction; the T.sub.W is made large so as 
to permit clear distinction of pulses; the difference between the 
T.sub.min and the T.sub.max is made small so that synchronization can be 
easily obtained; and the T.sub.max is made small to reduce the low 
frequency component in consideration of the foregoing points. 
Another object of the invention is to make the magnetization inversion 
interval long and to prevent mutual interference between the magnetic 
transitions due to the magnetization inversions before and after that 
interval and thereby to prevent the occurrence of errors upon reproduction 
and decoding. 
Still another object of the invention is to enlarge the demodulation phase 
margin (T.sub.W) (which will be explained later) upon reproduction, to a 
recording wavelength and thereby to prevent the occurrence of the 
foregoing errors. 
Still another object of the invention is to make the recording wavelength 
small as compared with the period of a clock signal for demodulation which 
is produced from the reproduction signal and thereby to accurately produce 
a clock signal from the reproduction signal. 
Still another object of the invention is to make the ratio between the 
maximum value and the minimum value of the magnetization inversion 
interval small and to also make the waveform interference (called the 
pattern peak shift) of the reproduction signal small and thereby to 
prevent the occurrence of the foregoing errors. 
Still another object of the invention is to provide a data processing 
apparatus having a code converter which can be easily constituted by a 
programmable array logic. 
Still another object of the invention is to provide a data processing 
apparatus which produces a DC-freed code. 
Still another object of the invention is to provide a data processing 
apparatus which produces suitable codes due to a change-over of tables 
upon coupling of codes in consideration of the code before or after those 
codes. 
Still another object of the invention is to provide a data processing 
apparatus which produces further DC-freed codes using a programmable array 
logic. 
Still another object of the invention is to provide a data processing 
apparatus which has the codes corresponding to data in a table and codes 
the data by respectively performing the coordinating processes. 
Still another object of the invention is to provide a data processing 
apparatus which has the codes corresponding to data in a table and codes 
the data by respectively performing the coordinating processes and thereby 
producing the further DC-freed codes.