The AFDS discrete word 2 has this data:
-LNAV ENGAGE
-V/S ARM
-VOR/LOC ARM
-G/S ARM
-FLARE ARM
-CWS ROLL
-CWS PITCH
-SINGLE CH
-TO/GA
-V/S ENGAGE
-ALT HOLD
-ALT ACQ
-HDG SEL
-VOR/LOC ENGAGE
-G/S ENGAGE
-FLARE ENGAGE.
The AFDS discrete word 3 has this data:
-IAS/MACH select
-Altitude hold (MCP or VNAV)
-Altitude acquire (MCP or VNAV).
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CDS -- AUTOFLIGHT INTERFACES
The AFDS discrete word 4 has this data:

-Altitude alert flash -Test display -G/S deviation warn
- LOC deviation warn 
- CMD-A 
- CMD-B 

-F/D A ON -F/D B ON -VNAV SPD -VNAV PTH.
The DEUs use this data from the FCCs to show flight director commands and DFCS status on the displays.
The FCCs use engine N1 from the DEU general purpose bus for the speed trim and the flight control neutral shift functions. DEU discrete data also shows the FCCs which DEU sends data to which display unit.
Autothrottle Computer
The autothrottle computer sends this data to the DEUs as a discrete word on an ARINC 429 bus:
-ARM
-GA
-MCP SPD
-A/T LIMIT
-FMC SPD
-N1
-RETARD
737-600/700/800/900 TRAINING MANUAL

-TEST.
The autothrottle computer sends a ground discrete to the DEUs for the throttle hold mode.
The DEUs use this data to show the active autothrottle mode in the flight mode annunciator on the primary flight displays. The A/T LIMIT annunciation shows when FMCS thrust mode annunciation data is not valid.

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31-62-00-111 Rev 1 07/05/2001

AUTOTHROTTLE  DEU 2 
COMPUTER 
CDS - AUTOFLIGHT INTERFACES 

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CDS -- HYDRAULIC AND LANDING GEAR INTERFACES Hydraulic System Pressure
Hydraulic system A pressure transmitter sends hydraulic pressure as an analog signal to DEU 1. Hydraulic system B pressure transmitter sends an analog signal to DEU 2.
The DEU sends an 8 vdc reference voltage to the transmitter and the resultant current flow represents the hydraulic pressure. The DEU then converts this current into a pressure value for display. Nominal current is 16 mA at a hydraulic pressure of 3000 psi.
The hydraulic system pressure data goes on the DEU cross channel bus so that both DEUs receive hydraulic system pressure from both system A and system B.
Hydraulic Fluid Quantity
The hydraulic fluid quantity transmitter/indicators for hydraulic system A and B send hydraulic fluid quantity as an analog signal to both DEUs.
The DEU sends an 8 vdc reference voltage to the quantity transmitter and the resultant output voltage from the potentiometer in the transmitter is proportional to the hydraulic quantity. The DEU then converts this voltage into a hydraulic quantity value for display. Nominal voltage is 0.8147 V/Vref for a FULL reservoir indication.
737-600/700/800/900 TRAINING MANUAL

Proximity Switch Electronics Unit
The proximity swich electronics unit sends a total of four ground discretes to each DEU. They are air ground signals from air/ground system 1 and air/ground system
2. These discretes are used for the display enable function within the DEUs and also flight leg counting within BITE.

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2

HYD SYSTEM A
PRESSURE TX

3 SYSTEM A HYDRAULICHYD SYSTEM A

PRESSUREFLUID QUANTITY TRANSMITTER/ INDICATOR
DEU 1

SYSTEM B HYDRAULIC3

PRESSURE
HYD SYSTEM B FLUID QUANTITY 2TRANSMITTER/ INDICATOR

HYD SYSTEM B
PRESSURE TX
PSEU
DEU 2
CDS - HYDRAULIC AND LANDING GEAR INTERFACES
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CDS -- AIR CONDITIONING AND PNEUMATIC INTERFACES General
The display electronic units (DEU) receive discretes from these air conditioning and pneumatic systems:
-Air conditioning relays
-Pack flow control and shutoff valves
-Bleed air isolation valve
-Air conditioning module.

The DEUs send the data out on the general purpose buses and the EEC/APU buses. This data is used by these airplane systems:
-Digital flight data acquisition unit
-Main engine electronic controls
-APU electronic control unit.

Air Conditioning Relays
The air conditioning relays send ground discretes to both DEUs. The DEUs use these discretes to determine the position of the left and right pack valve normal relays.
Flow Control and Shutoff Valves
　
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