TM 5-6675-320-14
aq. FET gate supplies.
The positive FET gate supply is a doubler and regulator,
producing an output which is maintained at a level 12 volts more positive than the
+34 volt main supply.
The nominal level is +46 volts.
The 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.
a r .
Power-Up reset circuit.
The reset circuit on the chart hold PCA A6 provides a
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-
p r o c e s s o r c i r c u i t s .
a s . E l e c t r o s t a t i c p o w e r s u p p l y .
The electrostatic power supply on PCA A6
develops a high voltage at a very low current to hold the chart against the platen.
T h i s i s a r i n g i n g c i r c u i t c h a r g i n g t w o p a r a l l e l c a p a c i t o r n e t w o r k s . T r a n s i s t o r Q 1 01
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-
citance to a high level.
When the charge on the inductor is greater than the charge
on 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
t o t h e p l a t e n .
The open circuit voltage to the platen is approximately 900 volts.
a t .
P e n l i f t d r i v e.
The pen lift drive is a switched current source providing
approximately 250 mA to the pen solenoid.
When 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.
4 - 3 . 3 H P - I B I n t e r f a c e,
T h e i n t e r f a c e p e r f o r m s f o u r m a j o r f u n c t i o n s : i n t e r p r e t i ng
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 1/0 and the HP-IB.
I t d e t e r m i n e s i f t h e c a l c u l a t o r i s r e q u e s t -
ing an 1/0 operation by monitoring the CFLG (Calculator Flag) line from the calcula-
tor command register.
I f t h i s s i g n a l i s t r u e , t h e p r o c e s s o r i s s u e s t h e a p p r o p r i a te
instructions to the other modules to decode and execute the requested 1/0 operation.
The processor monitors the status of the HP-IB by periodically sampling its control
lines (ATN, SRQ, REN, IFC, and EOI) and its transfer lines (DAV, NRFD, and NDAC) via
t h e d a t a i n p u t m u l t i p l e x e r.
I f a c o n d i t i o n i s d e t e c t e d t h a t r e q u i r e s a c t i o n ( f or
example, a require service message) the processor issues the appropriate
instructions to complete the operation requested.
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