DETAILED CIRCUIT DISCUSSION - TM-11-5805-688-14-10197

T.O. 31W2-2GSC24-2

TM 11-5805-688-14-1

NAVELEX 0967-LP-545-3010

5-363. The word 24 activity detector monitors the word

DIAGNOSTICS AND OVERHEAD switching capability,

24 output from the word 24 decoder and generates a

an active channel not fitted with a channel card would

word 24 error signal to the composite error detector

yield a high-level error signal, which would be applied to

when either the word 24 decoder or end-of-scan decoder

the channel input of multiplexer U3 to indicate a faulty

signals are missing. The detector can be set or reset by

diagnostic-error condition during the self-test mode.

signal ST2 or ERST as explained in paragraph 5-362.

Setting

the

appropriate

DIAGNOSTICS

AND

OVERHEAD switches to the OFF positions for these

5-364. The composite error detector generates OEG

channels prevents an undesirable self-test condition.

card diagnostic signal MTMOG to the display card when

a stuff error or W24 error signal is applied. Once the

5-367. Positive stuff request signals MPSTO1through

error input to the detector is removed, the detector output

MPST15from the active channels in the multiplexer are

returns to its no-error state. The detector circuits can be

applied through the ON positions of the switches (S1) to

set to the error state by self-test signal ST2- as explained

inputs on positive stuff multiplexer No. 1 (U3). Overhead

in paragraph 5-362.

address count signals MOHO through MOH3 select the

multiplexer channel that is interrogated and multiplexed

into a single positive stuff output data stream as positive

5-365. DETAILED CIRCUIT DISCUSSION.

stuff acknowledge signal MPSA. Signal MPSA is routed

to the GC/DM card. The signal is also applied to

5-366.

In certain unique system configurations, a

exclusive OR gate U8-6 in the diagnostic comparator

channel may possibly be active but not have a channel

circuit. As part of the card diagnostic function performed

card installed. Therefore, the 15 DIAGNOSTICS AND

during word 24, signal MPSA is applied through .inverter

OVERHEAD switches (S1) are provided on the OEG

U7-3 and is routed as signal MPSA to the display card.

card to prevent false channel card diagnostic error

Negative stuff request signals MNSTO1through

signals when the multiplexer is in the self-test mode.

MNST15are

processed

through

negative

stuff

The switch is set to the ON position for each active

multiplexer No. 1 (U5) to generate a single negative stuff

channel that has a channel card installed. In turn, the

output data stream as negative stuff acknowledge signal

switch associated with each active channel not having a

MNSA. Signal MNSA is routed to the GC/DM card.

channel card installed is set to the OFF position.

Settings of switches associated with inactive channels

5-368. Signals MPSA and MNSA are compared in the

may be in the ON or OFF positions, since inactive

diagnostic comparator circuit with their equivalent

channels are not sampled. In the self-test mode, each

diagnostic MPSA and MNSA signals from positive and

channel input to positive stuff multiplexer U3 that has the

negative stuff multiplexers No. 2 (U4 and U6). The

switch in the ON position receives the diagnostic error

compare function is performed by four exclusive OR

status from the associated channel card. Each channel

gates (U8).

When an error condition is detected

card input to multiplexer U3 that has the switch set in the

(mismatch), the exclusive OR gates cause flip-flop U15

OFF position receives a low-level self test signal ST2in

to generate a high-level Q output which, in turn, causes

the self-test mode, and a high-level no-error signal in

OEG card diagnostic signal MTMOG- to be generated

normal operation. A low-level diagnostic signal input to

from OR gate U13-4 in the composite error detector

multiplexer U3 is processed as a no-error condition in the

circuit.

overhead

diagnostic

function.

Without

the

5-96