Detailed Functional Description-continued

TM 11-7010-201-40-5/ET821-AA-MMI-050/E154 MTS/T O 31S5-2TSQ73-2-5

eight self-test signals, six card ID signals, ten state signals, six Y address signals, four X address signals, the enable TC

signal, and the data CK signal all enter the MTS test aid through connector J01. Each signal is used as an input to

individual lamp drivers. These lamp drivers (located on circuit board A01) are NAND gates with one active input. The

other input to each of the lamp drivers is floating, and is a logic high. in the driver. Since there is only one variable

signal entering these lamp drivers; the NAND gates are actually used as inverters. When the variable signal entering the

gate (from J01) is a logic high, the signal leaving the gate is a logic low. The output from each of the lamp drivers is

applied to pin 1 of the individual indicators. When pin 1 is a logic low, the indicator will light, as previously described.

There are 72 identical circuits on the circuit board that are controlled by the DATA/FUNCTIONAL/CONT switch

(SO1). These circuits activate the 72 indicators (numbered 1 through 72) on the MTS test aid front panel. To simplify

this discussion, only one of the circuits will be described in detail.

Each circuit is composed of two inverters and three lamp drivers. Three input signals from connector JO1 are used

by the circuit. Two of these signals, continuity in error (J01-184) and functional in error (J01-112) are inverted. The

inverted signals are used as one of the two inputs to their respective lamp drivers. The third input signal, data bit (J01-

35), is not inverted but is sent directly to a lamp driver as one of its two inputs. The other input to these three lamp

drivers is controlled by the DATA/FUNCTIONAL/CONT switch. This switch shorts two of its three terminals to ground.

The third terminal is allowed to float, and therefore applies a pull-up voltage to the appropriate lamp driver input. This

pull-up voltage is felt as a logic high by the lamp driver. Since the two pull-ups associated with the other two switch

terminals are shorted to ground, a logic low is felt on the input to the applicable lamp drivers. The output of the three

lamp drivers are ORed together and tied to an indicator. To light the indicator, any of the three lamp driver outputs must

be a logic low. To accomplish this, the lamp driver receiving a logic high signal from the DATA/FUNCTIONAL/CONT

switch must also receive a logic high on its other input terminal (from J01).

The circuit board also contains a quad 2-input NAND circuit which functions as a flip-flop. The flip-flop is controlled

by the action of SCP switch S05 (step clock pulse) and is a set-reset device. The output of the flip-flop is routed out of

the MTS test aid through J01-108.

SS toggle switch S03 (stop on error) provides a ground to J01-107 when in the up position. BCP toggle switch S04

(single step clock pulse) provides a ground to J01-109 when in the up position.

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