Cable Digital Processor 1A12A4 Circuit Functioning

TM 11-5820-695-35

(+5v). The output signal from A6 is coupled to the base

negative pulse output signal. Capacitor Cl is a supply

of Q1 through bias resistor R8. When the output from

voltage filter. The functions of capacitors C12 and C13

A6 is +5v, Q1 is turned on and output signal 1CRLFAIL

and resistors R18 and R19 at 48-channel baud

is logic zero (normal). Lamp DS1 is lighted because it

generator Al are similar to the functions of

has a ground connection through Q1. When the pcm

corresponding parts at A5.

signal fails, A6 times out and the output signal at pin 8

returns to Ov. Q1 is turned off and output signal

Lamp Driver. The -6 volt supply voltage

1CRLFAIL is logic one (alarm condition). Lamp DS1 is

through resistor R28 speeds up transitions from high

turned off but it has a quiescent current through resistor

(logic one) to low (logic zero) at the input of A10C.

R5 which keeps the filament warm. This reduces the

Resistor R29 provides a current to keep lamp DS1 warm

current surge through Q1, when Q1 and DS1 turn on.

when the output of A4A is high. When the output of

A4A returns to low, the current surge through A4A is not

Voltage Filtering Components.

Voltage

as great due to the lamp warming current.

filtering components L1 and C1, C2 and C3 limit the

coupling of switching transients and other stray signals

Voltage Filtering Components.

In the

to the power supply circuits.

synchronous

mode

(1A12A3)

voltage

filtering

components (L1 through L4 and C17 through C24) limit

2-44. Alarm Monitor 1A12A5 and 1A12A15 Circuit

the coupling of switching transients and other stray

signals to the power supply circuits. The +6 volt supply

Theory (fig. 533 and 5-33.1)

for A8 is derived internally by dividing the +12 volt

supply voltage. This is accomplished by resistor R20

The integrated circuits used in alarm monitor 1A12A5

and zener diode CR13. This voltage is filtered by

and 1A12A15 are shown functionally in figure 5-33 for

capacitor C14. In the asynchronous mode (1A12A14),

the synchronous mode and in figure 533.1 for the

the +5vdc supply voltage is filtered by L1 and C3, C4

asynchronous mode. Figures 533 and 533.1 also

and C5.

specify each integrated circuit type.

Figure 6-24

provides a circuit diagram for each type of integrated

2-43.

Cable Digital Processor 1A12A4 Circuit

circuit used in Radio Set AN/GRC-144. The complete

functional description of the alarm monitor is provided in

Functioning (fig. 5-32)

paragraphs 2-5f and g and 2-6h and i. Electrical

operation of discrete parts not discussed in paragraphs

Cable digital processor 1A12A4 contains integrated

2-5f and g and 2-6h and i is provided in a, b, and c

circuits designated Al through A6. Figure 5-24 provides

below which apply specifically to the synchronous mode

a diagram for each type of integrated circuit used. The

(1A12A5); however, they apply also to the asynchronous

complete functional description of cable digital

mode (lA12A15) since the only change is that the

processor 1A12A4 is provided in paragraph 2-5c.

reference designators of the logic circuits are different.

Electrical operation of discrete piece parts is provided in

The cable traffic detector is discussed in d (1A12A5)

subparagraphs below.

and d.1 (1A] 2A15) below. The circuit description for

voltage filtering components in the asynchronous mode

Level Converters. Resistors R1, R2, and

(lA12A15) is similar to that provided in e below for the

R3 of level converter 1 are voltage dividing resistors

synchronous mode (1A12A5).

that also provide impedance matching for the 1TRPCM

output signal. The logic zero output is 0 volts to 0.5 volt

Lamp Drivers. The lamp driver circuits

at 15.5 ohms impedance. The logic one output is 1.5

conduct 40 ma. to operate the 28 vdc lamps with

volts at 22 ohms impedance. In level converter 2,

standard logic inputs. Each circuit is a simple npn

resistors R9, R10 and All perform a similar function for

transistor inverter with a series 150 ohms collector

signal 1RRPCM.

current limiting resistor (required to limit the current

surge because of a cold filament when turning on the

Alarm Circuits. In alarm circuit 1, resistor

lamp). When the input is a standard logic one, the

R7 connects the +5v supply to A6 and capacitor C5 is a

transistor is saturated and the lamp driver provides

supply voltage filter. Resistor R4 and capacitor C4

maximum current (40 ma.). When the input is a logic

determine the time constant for monostable

zero, the transistor is cut off and the output is open

multivibrator A6 and thus determine the duration of the

(equal to lamp supply voltage).

logic one output (pin 8) when the input (pin 1) goes

negative. If the pcm signal is active, this occurs

constantly and the output of A6 remains at logic one

2-82

Change 1