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 DEU A - Block Diagram
 Figure 020 (SHEET 1)

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 DEU A - Block Diagram
 Figure 020 (SHEET 2)

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 DEU B - Block Diagram
 Figure 021 (SHEET 1)

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 DEU B - Block Diagram
 Figure 021 (SHEET 2)

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 (h) System Interface Circuitry The system interface circuits are under the control of the gate array. They provide the interfacing between the low-level parallel data and the connected equipments. The DEU internally use low-level parallel data. BITE circuitry is incorporated where necessary for monitoring the current in order to detect open and short-circuit fault conditions.
 1 Discrete Inputs and Outputs
_ Each DEU discrete input includes opto-coupled input-protection to avoid damage to the DEU if there is a faulty connected unit. Each input has its own defined characteristics according to the equipment it is interfaced. With each input is converted into Transistor Transistor Logic (TTL) levels and then connected to the gate array, where it is monitored. Opto couplers buffer TTL-Level outputs from the gate array to provide AC ground outputs. Further TTL-Level outputs from the gate array connect to 28 V DC drivers to give twenty open/28 V DC type short-circuit-protected outputs. Each driver is monitored for driver failure or output short circuit. If either occurs it is signalled to the gate array. The current-measurement-circuit for lamp-testing purposes measures the total current of these open/28 V DC outputs. This is also signalled to the gate array. The DEU can individually activate outputs and verify that the current drain is within given limits. It determines the high/normal/low resistance status of the connected load. Service bus 28 V DC is supplied from the power supply module to the discrete input/output circuits.
 2 DEU A Audio Outputs
_ Six audio channels are defined for the top line bus. One DEU A can accept two from these audio channels. The gate array directs these audio input signals to the respective channel 1 or channel 2 Digital to Analog (D/A) converter in the audio circuitry. It also connects the respective volume signal from the gate array to each D/A converter. Each D/A converter volume is controlled separately with commands from the bus. Each level controlled analog audio signal connects to a programmable filter. This is under control of gate array, which in turn receives filter control commands from the director. Separate power amplifiers amplify these signals for driving the loudspeakers. Each power amplifier is linked to the current measurement circuit. This measures the impedance of each loudspeaker separately. The result is sent via the gate array and bus driver to the director.
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 3_ DEU B Inputs and Outputs
 A DEU B receives digitized audio signals. The gate array
 transfers these signals to the D/A converter circuit. The
 analog signals are then filtered and pre-amplified and send to
 the handset. Audio signals (including dial tone) from the
 handset connect to a Dual Tone Multiple Frequency (DTMF)
 decoder and to a filter/amplifier A/D converter. The gate
 array transfers the data from the decoder to the director for
 dialling purposes. The digitized audio also connects to the
 gate array.
 An audio Input/Output (I/O) circuit test can be made. The
 audio output is switched through to a summer which adds the
 signal to the audio input. This is done via a command line
 from the gate array. An off-hook serving circuit also connects
 to the handset and has a connection to the gate array.
 4_ Miscellaneous Inputs and Outputs (DEU B)
 A serial RS232 interface is used to communicate between the
 gate array, the attendant indication panel and the aft
 attendant panel.
 A serial interface is also provided for separate testing of
 the emergency lighting power supply units.

 (2) Operation (Ref. Fig. 022, 023, 024)
 (a)
 CIDS Power-Up When the CIDS is powered-up or reset, the director follows a power-up routine. This includes the initialization and testing of each DEU and connected equipment. Each of the two DEU A PA amplifiers are assigned to one of the six topline audio channels. The gain and frequency response of each amplifier is set. The test results are transmitted to the director which compares them with its programmed data to decide on their OK/NOT OK status.
　
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