
W83877ATF
Publication Release Date: April 1998
- 15 -
Version 0.51
1.4 FDC interface, continued
SYMBOL
PIN
81
I/O
IN
cs
FUNCTION
INDEX
This schmitt input from the disk drive is active low when the head
is positioned over the beginning of a track marked by an index
hole. This input pin is pulled up internally by an approximately 1K
ohm resistor. The resistor can be disabled by bit 4 of CR6
(FIPURDWN).
Motor A On. When set to 0, this pin enables disk drive 0. This is
an open drain output.
MOA
79
OD
24
MOB
80
OD
24
Motor B On. When set to 0, this pin enables disk drive 1. This is
an open drain output.
Step output pulses. This active low open drain output produces a
pulse to move the head to another track.
Drive Select A. When set to 0, this pin enables disk drive A. This
is an open drain output.
STEP
82
OD
24
DSA
83
OD
24
DSB
84
OD
24
Drive Select B. When set to 0, this pin enables disk drive B. This
is an open drain output.
Write enable. An open drain output.
Write data. This logic low open drain writes precompensation
serial data to the selected FDD. An open drain output.
Reduced write current. This signal can be used on two-speed disk
drives to select the transfer rate. An open drain output.
Logic 0 = 250 Kb/s
Logic 1 = 500 Kb/s
When bit 5 of CR9 (EN3MODE) is set to high, the three-mode
FDD function is enabled, and the pin will have a different
definition. Refer to the EN3MODE bit in CR9.
Head select. This open drain output determines which disk drive
head is active.
Logic 1 = side 0
Logic 0 = side 1
Direction of the head step motor. An open drain output.
Logic 1 = outward motion
Logic 0 = inward motion
+5 power supply for the digital circuitry
WE
WD
85
86
OD
24
OD
24
RWC
87
OD
24
HEAD
88
OD
24
DIR
89
OD
24
V
DD
15,
56
GND
25,
40
65,
90
Ground