W83787IF Datasheet, PDF (72/123 Pages) Winbond – WINBOND I/O WITH SERIAL-INFRARED SUPPORT

W83787IF
Once this bit is set high, the FDC operates normally, but because pin WE is inactive, the FDD will not
write data to diskettes. For example, if a diskette is formatted with DISFDDWR = 1, after the format
command has been executed, messages will be displayed that appear to indicate that the format is
complete. If the diskette is removed from the disk drive and inserted again, however, typing the DIR
command will reveal that the contents of the diskette have not been modified and the diskette was
not actually reformatted.
The reason for this is that as the operating system (e.g., DOS) reads the diskette files, it keeps the
files in memory. If there is a write operation, DOS will write data to the diskette and memory
simultaneously. When DOS wants to read the diskette, it will first search the files in memory. If DOS
finds the file in memory, it will not issue a read command to read the diskette. When DISFDDWR = 1,
DOS still writes data to the diskette and memory, but only the data in memory are updated. If a read
operation is performed, data are read from memory first, and not from the diskette. The action of
removing the diskette from the drive and inserting it again forces the DSKCHG pin active. DOS will
then read the contents of the diskette and will show that the contents have not been modified. The
same holds true with write commands.
The disable FDD write function allows users to protect diskettes against computer viruses by ensuring
that no data are written to the diskette.
SWWP (Bit 4):
0
Normal, use WP to determine whether the FDD is write-protected or not
1
FDD is always write-protected
Media ID 1 Media ID 0 (Bit 3, 2):
These two bits hold the media ID bit 1, 0 for three mode
Floppy Boot Drive 1 Floppy Boot Drive 0 (bit 1, 0)
These two bits hold the value of floppy boot drive 1 and drive 0 for three mode
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Publication ReleaseDate:Sep 1995
Revision A1