Multiplex Communication; Wake-Up And Sleep; Fail-Safe - Honda EP3 Service Manual

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System Descriptions
The Multiplex Control System has four internal
functions:
. M u l t i p l e x i n g ( s e n d m u l t i p l e s i g n a l s o v e r s h a r e d
w t r e s )
. Wake up/sleep (runs at full power only on demand to
reduce battery draw)
. Fail-safe (fixes or ignores faulty signals)
. Self-diagnosis (Mode 1 for the system, Mode 2 for
i n p u t l i n e s )
The system controls the function of these circuits:
. E n t r y l i g h t c o n t r o l ( i g n i t i o n k e y l i g h t a n d c e i t i n g l i g h t )
. Wiper/washer intermittent wipe and park functions
. Keyless/power door lock
. Meter assembly, temperature gauge, and indicator
lights
. HVAC (compressor and fan control)
. K e y - i n r e m i n d e r
. H e a d l i g h t r e m i n d e r
. Seatbelt reminder
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Multiplex Communication
To reduce the number of wire harnesses, digital signals
a r e s e n t v i a s h a r e d m u l t i p l e x c o m m u n i c a t i o n l i n e s
r a t h e r t h a n s e n d i n g n o r m a l e l e c t r i c a l s i g n a l s t h r o u g h
i n d i v i d u a l w i r e s .
. The input signals from each switch are converted to
digital signals at the central processing unit (CpU).
. T h e d i g i t a l s i g n a l s a r e s e n t f r o m t h e t r a n s m i t t i n g
u n i t
t o t h e r e c e i v i n g u n i t a s s e r i a l s i g n a l s .
. The transmitted signal is converted to a switch signal
at the receiving unit, and it operates the related
component or monitors a swltch.
. There are exclusive communicalion lines between
the ECM, the gauge assembly, and the under,dash
fuse/relay box.
Wake-up and Sleep
The multiplex control system has "wake-up" and
"sleep" functions
to decrease parasitic draw on the
battery when the ignition switch is OFF.
. ln the sleep mode, the multiplex control unit stops
functioning (communication and CPU control) when it
is not necessary for the system to operate.
. As soon as any operation is requested (for example, a
door is unlocked), the related control unit in the sleep
mode immediately wakes up and begins to function.
. When the ignition switch is turned OFF, and the
driver's or front passenger's door is opened, then
closed, there is about a 10 second delay before the
control unit goes from the wake-up mode to the sleep
m o d e .
. lf any door is open, the sleep mode will not function.
. l f a k e y i s i n t h e i g n i t i o n s w i t c h , t h e s l e e p m o d e w i l l
not function.
. When in sleep mode, the draw is reduced from
70 80 mA to less than 10 mA.
Fail-safe
To prevent improper operation, the multiplex control
system has a fail-safe function. In the fail-safe mode,
the output signal js fixed when any part of the system
malfunctions (for example a faulty control unit or
c o m m u n i c a t i o n l i n e ) .
Each control unit has a hardware fail-safe function that
fixes the output signal when there is any CPU
malfunction, and a software fail-safe function that
i g n o r e s t h e s i g n a l f r o m t h e m a l f u n c t i o n i n g c o n t r o l u n i t
and allows the system to operate normally.