HP 13255 Technical Information page 30

132~5
Cartridge Tape MOdule
13255-91032/28
Rev AUG-01-7b
time is dlso 1 millisecond. Therefore, GAP is true 1 millisecond after
data stops until 1 millisecond into the next bloCK. The output of U13,
Pin 4 1s connected to Pin 10 of U12 and the outout of U13, Pin 6 is
connected to OR gate U12, Pin 9. This serves to quiet the DZX output
during gap time.
3.1.6 TACHOMET~R F~F.DBACK SELECT AND CONDITIONING CIRCUITS - R~AD/WRITE peA.
3.1.6.1 The tachometer feedback select and conditioning circuits condition the
inputs from the tachometers
by
filterlnq and
by
comparison and then
select the signal from the tachometer dssociated with the CTU Transport
that is selected.
3.1.6.2 The tachometer on the capstan drive motor is a variable reluctance type
which produces a sine wave output of approximately 300 millivolts peak-
to-peak at 10 inches per second tape speed. This signal is fed into
the ~ead/Write PCA. The signal has a 0.027 microfarad (C2 and C4) fil-
ter capacitor shunting it to roll off the output of the tachometer
above the frequencies of interest (4 kHZ).
A
tach signal then drives a
comparator (Ul, Pin b or Ul, Pin 4) with positive hysteresis (33 milli-
volts).
NAND
gates U11 select the siqnal TACH FREQ from the selected
CTU Transport. This signal drives a delay circuit producing the
DELAYED fACH signal.
3.1.7 AMPLIFIER SELECT LOGIC - R~AD/WRITE PCA.
3.1.7.1 The amplifier select logic determines which motor is to be driven based
upon Which CTU Transport is selected.
3.1.7.2 If the RUNG signal is lOw, then 1SEL and OSEL are high, inhibitinq the
motor drive circuitry. If RUNG is high, both gates of ut1 in this
block are enabled. If Unit 0 is selected (USO high) and a cartridge is
inserted 1n Unit 0 (CINO high), then OSEL will be lOw, selecting the
CTU drive c1rcuits associated with CTU Transport Unit O. On the other
hand, if Unit 1 is selected (USO low) and a cartridge is inserted in
unit 1 (CIN1 high), then lSEL will be lOw, selecting tne CTU drive cir-
cuIts associated with CTU Transpor.t Unit 1.