Mitsubishi Electric M4853, Руководство по обслуживанию

Страница: 31 / 108

8.0 RECORDING FORMAT
Data to be recorded on the floppy disk is grouped in various
blocks.
There are bits, bytes, sectors, tracks, and sides. The bits are
encoded onto the disk by three possible means: FM, M F M , or MM F M
techniques. These bits are c o l l e c t e d together in a certain
number of bytes per sector to define the actual recording format
used. All of this is defined by the host system; the disk drive
just records and detects flux reversals on the disk.
8.1 As stated before, there are three main methods of
e n c o d i n g bits on a f l o p p y disk. A l l h a v e s o m e
a d v a n t a g e s and d i s a d v a n t a g e s , but the g e n e r a l l y
accepted standard is MFM (also called Double Density).
8.1.1 FM (Frequency Modulation) encoding is shown in Figure
8-1. It is the simplest form of encoding, and may be
decoded by used of inexpensive one-shot multivibrators.
It can do this because each data pulse is between two
clock pulses, thereby rigidly defining the "read
window" very precisely.
Figure 8-2 Figure Read Encoding