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Floppy Disk Controller: Difference between revisions
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→Option bits: move "deleted sectors" explanation to its own section
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(→Bit SK: explain what SK bit actually does) |
(→Option bits: move "deleted sectors" explanation to its own section) |
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==== "Deleted sectors" ====
The "WRITE_DELETED_DATA" command can be used to create a deleted sector, and the "READ_DELETED_DATA" command can be used to read one back.
==== Option bits ====
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Value = 0x40. "MFM" magnetic encoding mode. Always set it for read/write/format/verify operations.
===== Bit SK =====
Value = 0x20. Skip mode. This skips "deleted sectors" (see explanation in section above).
▲Value = 0x20. Skip mode. This skips "deleted sectors". Deleted sectors is a legacy feature, dating back to the 1970s, when IBM data entry terminals stored a single database record in each (128 byte) floppy sector, and a record could be marked as deleted by writing a different address mark before the sector. This feature was almost never used with IBM PC and compatibles (except for occasional abuse by copy protection schemes). Few (if any) emulators emulate this functionality, and many late model FDCs didn't implement it.
Ignore this bit and leave it cleared, unless you have a really good reason not to.
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