Receiver control clocks

TM 11-5865-215-13

(1) Receiver control clocks. The clocks are derived from the

crystal-controlled oscillator consisting of Yl, U4, and associated

components on microprocessor CCA Al.. The resulting 1.67-MHz output

is applied to U5 on CCA A7. U5 divides the input by 4. U6 divides

the output from U5 to provide the clocks listed in table 5-9.

(2) Keyboard display and front panel lamp intensity control.

The front panel LAMP INTENSITY control knob (potentiometer R4) con-

trols the intensity of the front panel lamps. The regulator consists

of a voltage comparator, a regulator driver, and a chassis-mounted

series regulator.

The voltage comparator compares the control input with a reference

voltage and responds to this comparison by controlling the conduction

of the regulator driver. The regulator driver control the conduction

of the series regulator. The series regulator responds to high cur-

rent drive by providing more source voltage to the lamps (thus in-

creasing lamp intensity). Lower current drive results in lower con-

duction of the series regulator and deceased lamp intensity. Table

5-10 lists reference voltages, and the key components of the panel

and keyboard (display) lamp intensity regulator circuits.

The reference input voltage to voltage comparator U2 on CCA A7 is

derived from +-5.6 V Zener regulator VR1. When the instrument panel

intensity potentiometer is rotated so that the wiper arm is moved to-

ward ground, a more negative voltage is applied to the voltage compar-

ator control input. U2 responds by increasing the forward bias to

regulator driver Q2. The driver then increases conduction of series

regulator Q1, providing more of the +28 V to the panel lamps. The

more negative instrument panel intensity control also causes the out-

put of voltage comparator A7U3 to go more positive, thereby increasing

Receiver Control Clocks

Table 5-9.

Input

Output

frequency

Function

frequency

division

CCA Al microprocessor clock

1.67 MHz

None

CCA A3 conversion clock

26.kHz

CCA A5 write timer clock

1.3 kMz

128

CCA A5 output cycle clock

6.5 kHz

256

CCA A3 sweep/step rate clock

512

3.25 kHz

1.625 kHz

1024

.812 kHZ

2048

5-37