HP 13255 Technical Information page 34

132~5
Cartrldge Tape Module
13255-91032/32
Rev AUG-Ol-76
3.2.2 FP SWITCH - CARTRIUGE ELECTRONICS PCA.
3.2.2.1 The File Protect (FP) switch
(51)
is activated when the RECOFO tab on
the cartridge is in the record position. This allows the user to
inhibit accidental recording of data.
3.2.2.2 with the RECORD tab in the record position, contact is made between two
padS on the Cartridge flectronics PCA. This contact allows current to
flow through the center tap of the head which causes recording on the
tape. It contact is not made then data may not be recorded on the
tape, irrespective of whether or not the Read/Write circuitry is in the
Write mode.
3.2.3 LAMP DRIVER - CARTRIDGE ELECTRONICS PCA.
3.2.3.1 The lamp driver accepts the ground true Lamp (L) signal and drives the
lamp used as an indicator for the user. The state of the lamp is con-
trolled by the firmware.
3.2.3.2 The lamp driver circuit consists ot
051,
R3, R12, and 1/2 of Ul. when
the output of U1 is in the high state (lamp oft), R3 allows approxi-
matelv 40 rnA to flow through
OS1.
This current keeps the filament hot
so that the lamp turn on surge current (155 mAl is less than twice the
nominal current. When J2, Pin 9 is grounded, the output of Ul goes
low applying approximately 3.5 volts across the lamp. R12 limits the
current throuqh DS1 to achieve longer lamp life.
3.2.4 HOLE DETECT - CARTRIDGE ELECTRONICS PCA.
3.2.4.1 The hole detect circuitry consists of a pulse generator and diode
driver and a detection circuit. The hole detect circuit detects the
holes in the tape and provides a ground true signal (HOLE) that Is used
in the determination of BOT, load point (LP), early warning (EW), and
EOT. Holes are detected with an infrared emitting diode and a photo-
transistor. Most of the time the irradiance emitted
by
the diode is
blocked
by
the opaqueness of the tape. When a hole moves in the path,
the irradiance travels to the photo-transistor and activates it. The
infrared emitting diode in the hole detect circuit is not on contin-
uously, but is pulsed at approximately 13 kHz. By pulsing the diOde,
more output can be Obtained with less average current and power diSSi-
pation.