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4.0
CONTROL
INPUT SIGNALS
The control signaIs are of two types: those to be multiplexed in a multiple drive
system and those intended to do the multiplexing.
The signaIs to be multiplexed are WRITE GATE, HEAD SELECT 2°, HEAD
SELECT 2
1
,
HEAD SELECT 2
2
,
HEAD SELECT 23, DIRECTION IN, and
STEP. These Hnes are terminated with a removable 220/330 {} resistor pack.
The multiplexing signaIs are DRIVE SELECT l, DRIVE SELECT 2, DRIVE
SELECT 3, and DRIVE SELECT 4. These Hnes are terminated in a single flXed
220/330 {} resistor pack.
Control signaIs are transmitted across the driver/receiver combination illustrat-
ed in Figure 10. Control input signaIs are activated in accordance with the fol-
lowing specifications:
True: 0.0 VDC to 0.4 VDC at 1
=
-48 mAmp max.
FaIse: 2.5 VDC to 5.25 VDC at 1
=
+250 JLAmp (open collector)
Termination: 220/330 {} resistor pack
FIGURE 10:
Control Signais
Driver/Receiver
Combination
7438
20 FT. MAX
FLAT CABLE OR TWISTED PAIR
HEAD SELECT 20, 2
1 ,
2
2 ,
2
3
4.1
These signaIs aIlow the selection of each Read/Write head in a binary code se-
quence. The Hnes are numbered 0 through 3. HEAD SELECT Hne 2° is the least
significant Hne. When aIl HEAD SELECT Hnes are high on the interface, Head
o
is selected.
WRITE GATE
4.2
The active state of this signal, or low level, enables data to be written to the
disc and inhibits carriage motion if WRlTE FAULT is active on the receipt of
the first Step pulse. When inactive, or high, this signaI enables data to be trans-
ferred from the drive and enables Step pulses to move the heads. Heads may
not be switched while WRlTE GATE is active.
8T212 PRODUCT MANUAL/Rev. B
13
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