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The Interface Module controls the instrumentation by collecting information from
various sources and converting that information into gauge pointer information
which it then sends to the gauges. It is an environmentally sealed unit and it is usu-
ally mounted beneath the cab and against the frame rail. It is connected to the J1708
data bus, and to switches, sensors and pressure/vacuum hoses throughout the vehicle.
All gauge and display information is gathered by the Interface Module except:
•
Road Speed and Engine Hours - Road Speed and Engine Hours messages
are sent directly to the SMC over the J1708 data bus. The SMC also uses
road speed messages to compute mileage and display it on the odometers.
•
Select and Reset Input - These switched inputs are applied directly to the
SMC.
•
Clocks - Clock and Alarm Clock information is generated within the SMC.
•
Gauge Backlighting - Power for the gauge backlighting comes from an ex-
ternal dimming control and completely bypasses the Interface Module.
Hose connections to the transducer modules provide pressure or vacuum to the In-
terface Module. The Interface Module converts the pressure and vacuum signals to
data and places that data on the private data bus to drive the pressure gauges. Con-
nections are shown in Figure 3-3.
If an Air Filter Restriction gauge is present, its input must be connected to port 5A. If
a Fuel Filter Restriction gauge is present, its input must be connected to port 5B.
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