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Example 2: | CE330S (light passing through the notch |
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| is sensed and decoded as write protect) |
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| (Double side, Double density) |
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| Write enabled | Write protected |
| Front side | Front side |
| Light is interrupted by the label | |
| O | o |
| 0 | 0 |
Two types of write protection are used and attention must bepaid to the presience of the label because it may cause a wrong result if the label is used improperly.
5)Media recording methods
Two recording methode are used:
•FM method (Single density)
This method is called the freqency modulation (FM)
n 1 n n 0
C D C D C
or double frequency (DF). Clock and data are written on the media which requires that a clock bit that precede the data.
0 | I | 0 |
| n fL_JL_fl | JL |
D | C |
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(C: clock, D: data)
Waveforms of data written or read in the FM mode are shown below.
r*-
(WD) |
| D | C I) | C D | C | D | C | D | C | D |
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| T_JILJn | n |
| ILJin | n | i |
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Write data |
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| 1 | 0 | 0 | l— |
| i | 0 |
| 0 |
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Write current |
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| 1 | > Wrote | ||||
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Residual magnetic |
| •«— | »• | .«— | — »• | + |
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flux on the media |
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| y \ | /^v | ^s~\ |
| "^ | Xy |
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| J |
| r/ | \J |
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| Read | |||
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| vyr\ |
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Differentiate | ^ |
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waveform |
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Shaped waveform |
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| i | rni |
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Read data (RD) |
| fi_ii_n | n | fl_Jn_jn |
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Write current: The write data is input to the flipflop and is inverted each time a pulse is received to change the direction of writing current.
Read waveform: The peak of the waveform is detected at a change of magnetic flux. The waveform is than shaped to obtain read data identic it >.<_• tlirf write data. Data cycle will be 4/^s.