w83877atd Winbond Electronics Corp America, w83877atd Datasheet - Page 115

• Manufacturer Part Number: w83877atd
• Description: Winbond I/o
• Manufacturer: Winbond Electronics Corp America

Because 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.
This 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):
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
8.2.10 Configuration Register 9 (CR9),
When the device is in Extended Function mode and EFIR is 09H, the CR9 register can be accessed
through EFDR. The bit definitions are as follows:
PRTMODS2 (Bit 7):
This bit and PRTMODS1, PRTMODS0 (bits 3, 2 of CR0) select the operating mode of the
W83877ATF. Refer to the descriptions of CR0.
LOCKREG (Bit 6):
This bit enables or disables the reading and writing of all configuration registers.
EN3MODE (Bit 5):
0
1
0
1
Normal, use WP to determine whether the FDD is write-protected or not
FDD is always write-protected
Enables the reading and writing of CR0-CR45
Disables the reading and writing of CR0-CR45 (locks W83877ATF extension
functions)
7
6
5
4
default = 0DH
3
- 111 -
2
1
0
CHIP ID0
CHIP ID1
CHIP ID2
CHIP ID3
reserved
EN3MODE
LOCKREG
PRTMODS2
Publication Release Date: April 1998
W83877ATF
Version 0.51