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Chapter 5 Input/Output Interfaces
Compaq Deskpro 4000N and 4000S Personal Computers
First Edition – September 1997
5-12
5.3.1.2 Diskette Drive Interface Control
The BIOS function INT 13 provides basic control of the diskette drive interface. The diskette
drive interface can be controlled by software through I/O-mapped registers listed in Table 5-7.
Table 5–8
. Diskette Drive Controller Registers
Table 5-7.
Diskette Drive Interface Control Registers
Primary
Address
Alternate
Address Register R/W
3F1h 371h Media ID R
3F2h 372h Drive Control W
3F4h 374h Main Status R
3F5h 375h Data R/W
3F7h 377h Drive Status
Data Transfer Rate
R
W
The base address (3F1h or 371h) and enabling of the diskette drive controller is selected through
the Function Enable Register (FER, addr. 399.00h) of the 87307 I/O controller. Address selection
and enabling is automatically done by the BIOS during POST but can also be accomplished with
the Setup utility and other software.
The following paragraphs describe the diskette drive interface control registers.
Media ID Register, I/O Port 3F1h/371h (Read Only)
Bit Function
7..5 Media Type:
xx1 = Invalid
000 = 5.25 inch drive
010 = 2.88 MB (3.5 inch drive)
100 = 1.44 MB (3.5 inch drive)
110 = 720 KB (3.5 inch drive)
4..2 Reserved
1,0 Tape Select:
00 = None 10 = Drive 2
01 = Drive 1 11 = Drive 3
Drive Control Register, I/O Port 3F2h/372h (Write Only)
Bit Function
7,6 Reserved
5 Drive 2 Motor
0 = Off, 1 = On
4 Drive 1 Motor
0 = Off, 1 = On
3 Interrupt / DMA Enable
0 = Disabled, 1 = Enabled
2 Controller Enable
0 = Reset controller, 1 = Enable controller
1,0 Drive Select
00 = Drive 1
01 = Drive 2
10 = Reserved
11 = Tape drive