::.. Floppy Sector Layout ..::
| Sector Layout |
|---|
| Sector Layout (Details) | |
|---|---|
| Function | Explanation |
| Preamble | 16 bytes of all zeroes; used to synchronize the controller for the following data fields. |
| Sector Address | Single byte having the most significent bit
equal to a "1" for a start bit, followed by two zeroes
The least significant five bits (A4...A0) contain the sector address.1 0 0 s s s s s= Sector Address 0-1FHThe sector count is 0 to 31 in decimal (or 00H to 1FH in hex) |
| Track Address | Single byte containing the track address in
the least significant seven bits A6...A0.0 t t t t t t t= Track Address 0-7FHThe track count is 0 to 76 in decimal (or 00H to 4CH in hex). Values above 76 (4CH) are invalid. |
| Data Block | 128 bytes of data stored by the user; may be in any binary or ASCII form. |
| Linkage - BCKPTR | 2 bytes Pointer to the preceding sector of data in the file (Backward Pointer). The pointer is composed of the sector and track addresses previously described. |
| Linkage - FORPTR | 2 bytes Pointer to the succeeding sector of data in the file (Forward Pointer). The pointer is composed of the sector and track addresses previously described. |
| CRC | The 2 bytes Cyclic Redundancy Check word is the output of the CRC generator contained in the controller. It is a checksum for the sector and track addresses, data block and linkage words. |
| Postamble | Is composed of a series of zeroes written after the CRC word to provide a protection gap after the valid data fields of the sector. |
Bit and byte order
During a write operation, bit cell 0 of each byte, is
transferred to the disk drive first with bit cell 7 being
transferred last.
The CRC word is written in the order LSB first, then MSB.
The Linkage Pointers are written in the order Sector Address first, then Track Address.
When data is read back from the drive, bit cell 0 of each byte
will be transferred first with bit cell 7 last. The CRC word is read in the order LSB first, then MSB.
The Linkage Pointers are read in the order Sector Address first, then Track Address.
