(b)
 DEU A Power-Up Tests These are tested at this stage

 1 Discrete outputs
_
 -All discrete outputs are switched to the passive state. Then each output is activated separately and looped back to the DEU gate array and measured. All the discrete outputs are then switched to the active state. The director checks that all the DEU current-sensing bits are activated. There is no test available for the opto-coupled outputs.
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 DEU Connection to Data Bus Power Supply and Address Coding
 Figure 022

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 INTENTIONALLY BLANK

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 DEU A - Connections to Cabin Systems Figure 023 (SHEET 1)
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 DEU A - Connections to Cabin Systems Figure 023 (SHEET 2)
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 DEU B - Connections to Cabin Systems Figure 024 (SHEET 1)
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 DEU B - Connections to Cabin Systems Figure 024 (SHEET 2)
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 2_ Discrete inputs
 - The director checks that no discrete inputs are active. Some
 input circuit failures cannot be detected by the director.
 These failures are only apparent when the appropriate input
 is activated. It is also possible that a fault in equipments
 connected to the director to mistaken for a faulty input
 circuit.
 3_ PA amplifier volume control, frequency control and audio
 output
 - The director generates a test signal, and the DEU audio
 outputs are monitored for correct action of the respective
 circuits. These tests are only done if a loudspeaker is
 connected.
 4_ No smoking, fasten seat belt, return to seat and passenger
 call lamps (not applicable for LED NS/FSB signs)
 - All lamp-outputs are set to OFF. The director controls the
 DEU's current-limit threshold for the lamp drivers. It also
 commands the DEU to turn on one lamp at a time. In this way,
 any open-circuit lamps are detected. This test also detects
 a failed current-detector.
 5_ The DEU A power supply, gate array, bus interface and BITE
 status are also checked.
 - The major DEU tests are continuously done for the whole time
 that the CIDS is switched on. In normal operation the
 director transmits information continuously to the DEUs.
 When a DEU is addressed, it must respond with a parity
 bit-coded message. If this response message is absent (or
 the parity bit is wrong for a minimum of 4 transmissions),
 then the DEU is declared to be unserviceable.

 (c) DEU B Power-Up Tests These are tested at this stage
 1 Discrete outputs, as for DEU A described in paragraph
_ 6.B.(2)(b)-1.
 2 Discrete inputs, as for DEU A described in paragraph
_ 6.B.(2)(b)-2.
 3 Audio Input/Output. The DEU B is commanded to perform a
_ loop-back operation, where the handset output is electronically connected to the handset input. The director transmits a test signal to the DEU B. After all the audio circuitry of the DEU B have processed this signal, it is
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 transmitted back to the director. The director can analyse the
 signal for frequency response and audio level. The test is
 also automatically performed, when a handset is unhooked.
 Signal-to-noise ratio, total distortion, and handset supply
 are not tested.
 4_ Serial Input/Output. Under control of the director, several
 types of tests are performed to check for faulty operation:
 - the register read/write test,
 - the timing test,
 - the status bit test,
 - the parity bit test,
 - the data loopback test (in conjuction with the connected
 hardware).
 The results of the loopback test assume the connected device
 is operational.
 5_ EVAC indicator lamp. As for discrete outputs described in
　
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