TM 5-1260-206-34
drop below 6 to 8 volts peak-to-peak. T o clear this condition the output
at TP3 must be restored to the proper level and a CLEAR LOCKOUT pulse
from the D card must be present. A n o t h e r input to the circuit is the
SAMPLE IND pulse from the G card. This pulse is generated on an 1/0
command to the calculator. I t is this input that sounds the sonalert when
any button on the DIC is pressed. The third input is the HOLD IND signal
from the D card. This input is not used and is disabled on the D card.
X-Y Axis Analog - t o - D i g i t a l C o n v e r t e r C i r c u i t r y - The analog-to-digital
converter converts the amplitude-modulated analog inputs from the 0MS
data grid to a phase-modulated digital signal. The X = O, X = 90,
Y = 0O , a n d y = 90 component signals from the OMS are fed to the analog
printed circuit card where they are changed to digital signals (X GRID
and Y GRID). These low level signals (millivolt range) from the OMS data
grid increase and decrease in amplitude as the cursor coil is moved
(amplitude modulated). The gain and phase of these signals are adjusted
by R34 and R40 for the X-axis and R65 and R70 for the Y-axis. These
signals are then summed, producing the output at TP3 or TP7. T h i s signal
is an 18 to 20 volt peak-to-peak phase modulated sine wave. The output
amplitude is adjusted by R43 or R72 and is dependent upon the height of
t h e cursor coil from the data grid surface ; when the cursor is raised the
s i g n a l amplitude drops. The signal is then converted from analog to
d i g i t a l . The output of the first stage seen at TP4 or TP8 is a 10 volt
peak-to-peak clipped sine wave. T h e last stage is a switching amplifier
converting the signal to a 5-volt square wave (X GRID or Y GRID). The
square wave is a phase-modulated signal containing cursor positional
information.
T h i s signal is sent to the X-axis (B) or Y-axis (C) card.
(4) Axis (B and C) Cards - The two identical axis cards provide the
following:
Count disable logic
Clear logic
Determine the incremental change in the X or Y position of
t h e cursor coil.
The axis card installed in the B position operates on the X axis; the axis
card in the C position operates on the Y axis. The circled numbers are keyed
C o u n t Disable Logic Circuitry - The count disable circuit disables the
position (X or Y) detector whenever SYNC goes low. It prevents circuit
o p e r a t i o n when cursor coil lockout detector is activated. The HOLD IND
i n p u t is not used.
C l e a r Logic Circuitry - The clear logic circuit resets position (X or Y)
detector when CAL input from D card goes low in the presence of the 30-Hz
CP4 clock. This produces a 15-Hz, 10-nanosecond CLEAR pulse which is
a p p l i e d to the position detector circuitry.
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