Acura 2002 RSX Service Manual page 1326

Multiplex Gontrol System
System Descriptions
The multiplex 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 ( 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 r r e s )
. Wake up/sleep (runs at lull 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 l i n g l i g h t )
. Wiper/washer (intermittent wipe and park functions)
. Interlock system
. Keyless/power door lock
. G a u g e a s s e m b l y , t e m p e r a t u r e 9 a u g e , 8 n d i n d i c a t o r
l i g h t s
. HVAC (compressor and fan control)
. Key-in reminder
. Lights-on reminder
. Seat belt reminder
22-174
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
rather than sending normal electrical signals through
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).
. Thedigital signalsare sent from the transmitting unit
to the receiving unit as serial signals.
. The transmitted signal is converted to a switch signal
at the receiving unit, and it operates the related
component or monitors a switch.
. There are exclusive communication lines between
the ECI\4/PCM, the gauge assembly. and the under-
dash fuse/relay box.
Wake-up and Sleep
The multiplex control system has "wake-up" and
"sleeD" functions to decrease
Darasitic draw on the
battery when the ignition switch is OFF.
. In 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 40 second delay before the
control unit goes from the wake-up mode to the sleep
mode,
. lf any door is open. the sleep mode will not function.
. lf a key is in the ignition switch, the sleep mode will
not function.
. When in sleep mode, the draw is reduced {rom-70-80
mAto 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 when any part of the system
malfunctions (for example a faultv 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
ignores the signal from the malfunctioning control unit
and allows the system to operate normally.