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MFM
,MFM is an acronym for "Modified Frequency Modulation" and is a data encoding used on floppy discs. It is used by the [[NEC 765]].
MFM is stored as flux transitions on the disc. The flux transitions are converted by the read/write head into a 1 or 0.
MFM stores data as a stream of bits with cells which contain a data bit and a clock bits bit. The data separator synchronises to a continuous pattern of zeros, and when synced, will transmit data and clock bits interleavedto the FDC as separate signals. Clock bits are transmitted first and their The value of a clock bit is the NOR of the previous data bit and the current data bit. Data is transmitted starting with bit 7 down to bit 0.
e.g.
Each clock and data bit on disc is 2microseconds in duration which means a full byte is 32 microseconds (2 * 16 bits).
