TM
11-5835-243-34/EE641-AA-MMl-010/E154
MTT/TO
31S3-4-110-1
b. Local Control Logic. The local control logic
write logic and turning on the front panel FILE
consists of combinational gating which decodes the
PTCT indicator via the low FILE PTCT LT line.
When the detent is not in the protected position, the
DR CL INTLK (door closed interlock), CRTG IN PL
contacts of switch A8S2 are open, and the write
INTLK (cartridge in place interlock), RWND SW
logic is enabled. A low level on the WR PERMIT
(rewind switch), RWND CMD (rewind command),
line to the interface indicates that a write operation
SEL CMD (selected command), and PRESET lines.
can be performed. When the W R RGT RESET line
When power is first applied, time delay Q1 and
from the interface goes low, voltage comparator
associated circuitry hold the PRESET line low. This
AR1 inverts the signal, forming WR RST CMD
inhibits the write logic and holds SEL-RDY
which is input to the write logic as a high pulse. This
(selected-ready) low for 500 ms. while the motion
signal is ANDed with SEL-RDY, generating the
control and data registers are reset (RESET is low,
high WR RST pulse which resets the write data
WR RST and RD RST are high). At the end of the
registers (J-K flip-flops U8, U9) on the digital
delay PRESET goes high, indicating that the
read/write circuit cards. The registers are also reset
initialization sequence is complete. When the tape
whenever WRITE goes high.
transport is selected (front panel ADDRESS switch
d. Read Logic. The read logic consists of one
setting corresponds to tape transport address), the
shots U4, U10 and associated gating elements
SEL line is high at the input to voltage comparator
AR1. At the output of AR1 the inverted SEL forms
which provide timing and selective output gating.
Data will be read from tape when the external
SEL CMD which is used on the digital read/write
control signal RD ENBL is low and tape speed is
logic circuit cards to enable the output gating logic
22.5 ips (FAST CMD is low). The low level RD
ENBL (read enable) is inverted by voltage com-
enable status gating U16 and U17, and set a low
parator AR1 to form RD CMD which is gated with
level on the SEL STAT line, acknowledging that the
the low FAST CMD to generate RD RST (read
tape transport is selected. With the SEL input high,
reset). Data output is inhibited when either RD
a tape cartridge in place, and the access door closed,
ENBL or FAST CMD is high. This condition causes
the CRTG IN PL INTLK, DR CL INTLK, and SEL
RD RST to go high, which clears the RZ and deskew
CMD lines are high, which raises the SEL-RDY line
flip-flops on the digital read/write circuit cards (para
high. The high SEL-RDY enables the write logic
and the tape motion command decode logic and sets
read/write circuit cards are inverted and used to
the RDY STAT line low. This indicates that the
trigger one-shot U4. The one-shot generates high
tape transport is not rewinding and is ready to
level pulses (23.4 microseconds wide) which are
receive remote commands and to transfer data.
inverted and output as RD CLK. The clock rate is a
RWND SW is a local control signal initiated by the
nominal 20 kHz (50 microseconds) at the tape speed
front panel RWND switch. When the switch is
22.5 ips. The inverted output of U4 is ORed with
depressed, rewind flip-flop U11 generates the low
FST CMD to trigger dual one-shot U1O which
level RWND FF signal which is output to servo
generates the two-microsecond wide, high level
control circuit card A5 as FAST RVS (para 2-9).
STROBE pulses. At the normal tape speed of 22.5
c. Write logic. Data can be written on tape when
ips STROBE is delayed 36 microseconds from the
the external control signal WR ENBL (write enable)
leading edge of the NODE input. When in the search
is low, the WR PERMIT SW line is high, and the
mode speed of 45 ips, STROBE pulses are generated
local control logic is indicating ready status (para b,
12.5 microseconds from the leading edge of the
above). Voltage comparator AR1 inverts WR ENBL
NODE input. STROBE pulses are routed to digital
forming WR ENBL CMD which is gated by U12
read/write circuit card (A3) and used to generate the
(part of write logic) with PRESET, WR PERMIT
RD STROBE output to the interface.
SW, and SEL-RDY. A high level on these four lines
e. Tape Motion Command Decode Logic. The taps
generates a low on the output of U12 (WRITE)
motion command decode logic consists of BCD to
which is applied to ramp generator Q2, Q3. The low
decimal decoder U 13 and associated combinational
level on the base of Q2 turns on switch Q4 which
gating. External control signals and tape status
connects the center tap of the write and erase head
signals are decoded by the logic to generate tape
windings to +5 vdc. The signal WR PERMIT SW is
motion commands which are used on the servo
derived from the write permit switch A8S2 located
circuit card (para 2-9). Tape status signals BEG
on the tape deck assembly. This switch is actuated
HOLE (beginning hole), BOT (beginning of tape),
by a rotary detent on the tape cartridge. When the
EOT FF (end of tape flip-flop), and END HOLE are
detent is in the protected position (PROT), the
generated on the servo control circuit card in
normally closed contacts of the switch connect the
response to signals from sensors located on the tape
WR PERMIT SW line to ground, inhibiting the
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