
1.0 Signal/Pin Connection and Description
(Continued)
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Revision1.2
P
1.4.6
Floppy Disk Controller (FDC)
Signal
Pin(s)
I/O Buffer Type Power Well
Description
DENSEL
74
O
O
2/12
V
DD
Density Select.
Indicates that a high FDC density data rate (500
Kbps, 1 Mbps or 2 Mbps) or a low density data rate (250 or 300
Kbps) is selected.
DIR
65
O
OD
12,
O
2/12
V
DD
Direction.
Determines the direction of the Floppy Disk Drive
(FDD) head movement (active = step in; inactive = step out)
during a seek operation.
DR1
DR0
70
67
O
OD
12
, O
2/12
V
DD
Drive Select.
Decoded output signals in Two-Drive mode or
encoded signals in Four-Drive mode. Controlled by bits 1 and 0 of
the Digital Output Register (DOR).
DRATE0
73
O
O
3/6
V
DD
Data Rate.
Reflects the value of bit 0 of the Configuration Control
Register (CCR) or the Data Rate Select Register (DSR), whichever
was written to last.
DSKCHG
57
I
IN
T
V
DD
Disk Change.
Indicates if the drive door has been opened.
HDSEL
58
O
OD
12
, O
2/12
V
DD
Head Select.
Determines which side of the FDD is accessed.
Active low selects side 1; inactive selects side 0.
INDEX
72
I
IN
T
V
DD
Index.
Indicates the beginning of an FDD track.
MSEN0
45
I
IN
T
V
DD
Automatic Media Sense.
Identifies the media type of the floppy
disk in drives 1 and 0 (if the drives support this protocol).
MTR1
MTR0
66
71
O
OD
12
, O
2/12
V
DD
Motor Select.
Active low, motor enable lines for drives 1 and 0,
controlled by bits D7-4 of the Digital Output Register (DOR). MTR0 is
used to decode DR1 and DR0 in Four-Drive mode.
RDATA
59
I
IN
T
V
DD
Read Data.
Raw serial input data stream read from the FDD.
STEP
64
O
OD
12
, O
2/12
V
DD
Step.
Issues pulses to the disk drive at a software programmable
rate to move the head during a seek operation.
TRK0
61
I
IN
T
V
DD
Track 0.
Indicates to the controller that the head of the selected
floppy disk drive is at track 0.
WDATA
63
O
OD
12
, O
2/12
V
DD
Write Data
. Carries out the pre-compensated serial data that is
written to the FDD. Pre-compensation is software selectable.
WGATE
62
O
OD
12
, O
2/12
V
DD
Write Gate.
Enables the write circuitry of the selected FDD.
WGATE is designed to prevent glitches during power-up and
power-down. This prevents writing to the disk when power is
cycled.
WP
60
I
IN
T
V
DD
Write Protected.
Indicates that the disk in the selected drive is
write protected.