Multiplex Control System Description - Honda 2002 Accord Manual

Multiplex Control System
System Description
The m u l t i p l e x Control System has four internal
f u n c t i o n s :
• M u l t i p l e x i n g (send multiple signals over shared
w i r e s )
• W a k e up/sleep (runs at full power only on d e m a n d to
reduce battery draw)
• Fail-safe (fixes or ignores faulty signals)
• Self-diagnosis (Mode 1 for the system, Mode 2 f o r
i n p u t lines)
The s y s t e m controls the function of the following
circuits
• Engine Oil Pressure Indicator
• Seat Belt Reminder
• Lights-on Reminder
• Key-in Reminder
• Key Light T i m e r
• Dash Lights Brightness Control
• Entry Light Control (EX, SE) (ignition key light and
ceiling light)
• A u t o m a t i c Lights-off (EX)
• Power Door Locks
• Power W i n d o w (including key-off timer operation)
• W i p e r / W a s h e r (including speed responsive
intermittent wiper)
• Keyless Entry/Security A l a r m (EX, SE)
• Interlock system (see page 14-144).
M u l t i p l e x Communication
To reduce the number of wire harnesses, digital signals
are sent via shared multiplex c o m m u n i c a t i o n lines
rather t h a n sending normal electrical signals t h r o u g h
individual wires.
• The input signals f r o m each switch are converted t o
digital signals at the central processing unit (CPU).
The digital signals are sent f r o m the transmitter unit
to the receiver unit as serial signals.
• The transmitted signal is converted to a switch signal
at t h e receiver unit, and it operates the related
c o m p o n e n t .
• There are exclusive communication lines between
each of the multiplex control units:
- Door «-» Driver's (between the door and the driver's
m u l t i p l e x control units) Wire color: BRN
- Driver's <-» Passenger's (between the driver's and
the passenger's multiplex control units) Wire color:
PNK
The control units always communicate via these lines
w h e n the system is operating, and they stop
c o m m u n i c a t i n g w h e n the system is OFF.
Wake-up and Sleep
The multiplex control system has " w a k e - u p " and
" s l e e p " functions to decrease parasitic draw on the
battery w h e n the ignition switch is OFF.
• In the sleep m o d e , the multiplex control unit stops the
functions (communication and CPU control) when it
is not necessary for the system to operate.
• As soon as any operation is requested (for example,
door is unlocked), the related control unit in the sleep
mode immediately wakes up and begins to function.
This control unit also sends a wake-up signal to the
other control units via the communication lines.
• W h e n the ignition switch is turned OFF, and driver's
or front passenger's door opened, there is about a 10
second delay before the control units go f r o m the
wake-up mode to the sleep mode.
• If any door is open, the sleep mode w i l l not function.
• If a key is in the ignition switch, the sleep mode will
not function.
• W h e n in sleep mode, the current d r a w is reduced
f r o m 7 0 - 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 is fixed w h e n any part of the system
malfunctions (for example, a faulty control unit or
communication line).
Each control unit has a hardware fail-safe function that
fixes the output signal w h e n there is any CPU
malfunction, and a software fail-safe function that
ignores the signal f r o m the malfunctioning control unit
and allows the system to operate normally.
22-136