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Theory of Operation
Also, ground voltage supplied to Q22 on the capstan
servo PCA holds switch Q20 on the capstan servo PCA
closed, grounding the input to motor drive amplifiers
Q2, Q4, and Q6. Ground voltage applied to Q19 on the
reel servo amplifier PCA, by the Tape Tension signal
and through the normally closed contacts of the LOAD
switch, cause it to close switches Q16, Q17, and Q20
on the reel servo amplifier PCA. With the inputs to the
reel servo amplifiers grounded, the reel motors are dis-
abled. Relay K1 is also kept deenergized through the
normally closed contacts of the LOAD switch and Q13
on the reel servo amplifier PCA. When the LOAD
switch is pressed, +5 volts is supplied through R9 and
R103 to activate the Tension signal to Q13 and Q19 on
the reel servo amplifier PCA. The high input to Q13
energizes relay K1. (Once energized, K1 remains ener-
gized, through R109, CR11, and Q13, until tension is
lost.) Pressing the LOAD switch also applies a high
input to Q19 on the reel servo amplifier PCA. Nand
gate Q19 holds Q16, Q17, and Q20 open if either of its
inputs are high. With K1 energized, both inputs to Q19
are high causing switches Q16, Q17, and Q20 on the
reel servo amplifier PCA to open. Thus, both require-
ments for enabling the reel servos (K1 energized and
switches Q16 and Q17 open) are met and the reel
servos tension the tape. Thus, with K1 energized and
Q20 on the reel servo amplifier PCA open, Q22 on the
capstan servo PCA (through Q21) opens Q20 on the
capstan servo PCA and enables the amplifier. With tape
tension established, tension arm switch W2S1 closes,
supplying a high input to terminal D of the Load For-
ward FF and to Q19 to the reel servo amplifier PCA.
2-26.
When the LOAD switch is released, the load point
search sequence is initiated. Load Latch (U1A and U2A) is
set. The output of the load latch is gated with REW (false)
to clock the Load Forward flip-flop (U12A). The LFWD
signal is gated with DELAY to provide the capstan servo
with the load point search command.
2-27.
The DELAY signal is generated by a delay circuit
located on the power regulator printed-circuit assembly. The
delay circuit provides a one-second delay when changing
from a high speed operation to a synchronous or load point
search mode.
2-28.
When the load point tab is detected (BOT), the
Load Forward flip-flop is cleared by LP through U16D and
U13B. Pressing RESET will also clear the Load Forward
flip-flop. When Load Forward is cleared, tape load point
search motion will stop. The edge transition of LDFD clocks
Load Complete flip-flop U12B. Except for a rewind condi-
tion, Load Complete remains set during normal operation
of the tape transport.
2-29.
Rewind flip-flop U6B is cleared by pressing the
REWIND switch when the unit is off-line, or by inter-
face command REW when the unit is on-line. When the
Rewind flip-flop is cleared, the Rewind Status flip-flop
(U4B and U3A) is set. This provides rewind status SRW
2-4
7970B/7970C
to the interface and rewind status to the control switch
assembly to illuminate the REWIND indicator.
2-30.
When the trailing edge of the load point tab is de-
tected during rewind the Load Point flip-flop is set and the
Rewind flip-flop is set through the rewind clock input (U6B-
11). Load point also gates U3B to prevent rewind commands
from clearing the Rewind flip-flop. With the Rewind flip-
flop set, the Load Forward flip-flop is set through gate U13A.
This starts the load point search mode.
2-31.
The control and status printed-circuit assembly con-
tains a unit select network that allows up to four units to be
controlled by one interface. The network consists of a
jumper (W1) and 5 connecting pins (OFF, 0, 1, 2, 3)_ The
position of the jumper determines the unit to be selected by
the interface. If the units connected to the interface are
equipped with the unit select switch option, the jumper
must be in the OFF position. With the jumper in the OFF
position the select match circuitry of the control and status
printed-circuit assembly is disabled. If the tape units are not
equipped with the unit select switch option, the jumper
must be connected to positions 0 through 3 depending upon
unit designation.
2-32.
The unit select command from the interface
(CSO, CS1, CS2 or CS3) is gated with ON-LINE to
generate SOLA and SOLB (selected and on-line). The
SOLA condition allows status signals to be supplied to
the interface. The SOLB condition is gated with COMP
(load sequence completed) to generate EXT (external
control). The EXT condition allows interface commands
to be processed. The OFF-LINE command from the
interface does not require the EXT condition. The OFF-
LINE command is gated with the unit select command
to clear the On-Line latch (U1D and U2B).
2-33.
The Rewind command (REW) from the interface is
gated with EXT to clear (assert) the Rewind flip-flop (U6B),
provided that tape is not at load point. The forward, reverse,
and high-speed (FWD, REV and HIGH SPEED) are gated
to provide motion commands to the tape transport servos
and data circuits.
2-34.
All status signals to the interface are gated with
SOLA. The load point status (SLP) indicates that the tape
unit is at load point (load point tab under photosense head).
The end-of-tape status (SET) indicates that the tape is at or
beyond the end-of-tape tab. The rewind status (SRW) indi-
cates that the tape is rewinding or in an automatic load
point search operation. The ready status (SR) indicates that
the tape unit is selected, on-line, and that the load sequence
is complete (not rewinding and not in a load point search
mode). The on-line status (SL) and file protect status (SFP)
indicate that the. unit is on-line, and that the tape reel in-
stalled on the supply reel hub is not equipped with a write
enable ring.
Part 2
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