TM 5-6675-323-14
a q . F E T g a t e s u p p l i e s . The positive FET gate supply is a doubler and regulator,
p r o d u c i n g an output which is maintained at a level 12 volts more positive than the
+ 3 4 v o l t m a i n s u p p l y . T h e n o m i n a l l e v e l i s + 4 6 v o l t s . T h e negative FET gate supply
is a Zener-regulated supply producing a voltage which is 12 volts less negative
than the -34 volt supply. The nominal level is -22 volts.
P o w e r - U p r e s e t c i r c u i t . T h e reset circuit on the chart hold PCA A6 provides a
ar.
negative pulse 70 milliseconds in duration at power-up. This pulse disables the
balance circuits, motor drive circuits, and provides a reset pulse to the micro-
processor circuits.
as. Electrostatic power supply.
T h e electrostatic power supply on PCA A6
develops a high voltage at a very low current to hold the chart against the platen.
This is a ringing circuit charging two parallel capacitor networks. Transistor Q101
is switched on and off by the 20 kHz oscillator signal. The transistor base voltage
is controlled by U102 and Q102, while the emitter current is limited by resistor
R114. While Q101 is switched on, a ramp of current is created in the inductor L101.
When the transistor is turned off, current continues to flow, charging stray capa-
c i t a n c e t o a h i g h l e v e l . W h e n the charge on the inductor is greater than the charge
o n the capacitors C102 and C103, the diodes CR102 and CR103 conduct, charging
these capacitors.
Resistors R102, 103, 105, and 106 current limit the high voltage
to the platen. The open circuit voltage to the platen is approximately 900 volts.
P e n l i f t d r i v e . The pen lift drive is a switched current source providing
at.
a p p r o x i m a t e l y 2 5 0 m A t o t h e p e n s o l e n o i d . W h e n Q10 is switched on, the voltage is
applied to the solenoid, lowering the pen to the paper. When the transistor is
switched off, the pen is raised by spring action.
3-3.3 HP-IB Interface. The interface performs four major functions: interpreting
control bytes from the calculator, transferring data bytes from the calculator to
the HP-IB, transferring data bytes from the HP-IB to the calculator, and transfer-
r i n g s t a t u s i n f o r m a t i o n t o t h e c a l c u l a t o r . The processor monitors the status of
both the calculator I/O and the HP-IB.
It determines if the calculator is request-
ing an I/O operation by monitoring the CFLG (Calculator Flag) line from the calcula-
tor command register.
If this signal is true, the processor issues the appropriate
instructions to the other modules to decode and execute the requested I/O operation.
The processor monitors the status of the HP-IB by periodically sampling its control
l i n e s (ATN, SRQ, REN, IFC, and EOI) and its transfer lines (DAV, NRFD, and NDAC) via
the data input multiplexer.
If a condition is detected that requires action (for
example, a require service message) the processor issues the appropriate
instructions to complete the operation requested.
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