Honeywell BENDIX/KING KAP 140 Maintenance Manual page 86

4.3.13 COCKPIT SWITCHES INTERFACE TO THE KC 140
PIN
P1401 -- 9
P1401 -- 26
P1402 -- 22
P1402 -- 25
P1402 -- 27
P1402 -- 30
AP_DISC is a 28V/Open discrete input. AP_DISC is 28V when not pressed and open when
pressed. This switch is wired to supply 28V to the high side of the servo clutches and servo motor
drives. When the AP_DISC switch is pressed, the AP is disconnected and power to the servo
clutches and motors is removed. This has the effect of disabling the servos. The KC 140 will
register the switch as being not pressed when the voltage at the connector of the KC 140 is > 11V.
The KC 140 will register the switch as being pressed if the voltage at the connector of the KC 140
is < 2V or if the impedance to aircraft power is > 200Kohms. (This assumes 28V on the aircraft
power bus.)
The CWS input is an Open/Ground input. When the CWS switch in the cockpit is pressed, the CWS
switch grounds the input to the KC 140. While the CWS input is active, the servo clutches
disengage without disconnecting AP, allowing the pilot to control the aircraft. Once the CWS input
becomes inactive, the KC 140 synchronizes the pitch axis to current aircraft condition (e.g. to
current altitude, if in ALT mode).
TRIM_UP, TRIM_DN, and TRIM_ARM are Open/Ground inputs that are used by the KC 140 to
determine when manual electric trim has been requested. When TRIM_UP & TRIM_ARM are both
active (active is defined as that input being grounded), manual electric trim operation trims the
aircraft nose up. When TRIM_DN & TRIM_ARM are both active, the manual electric trim operation
trims the aircraft nose down. In some installations, the manual electric trim switch is constructed
in such a way that you will always have TRIM_ARM active before having either TRIM_UP or
TRIM_DN active.
STALL_WARNING is a Open/Ground input that is currently not implemented in any configuration
of the KAP 140 autopilot system.
4.3.14 DIMBUS INTERFACE (BACKLIGHTING BRIGHTNESS) TO THE KC 140
PIN
P1401 -- 12
The DIMBUS voltage from the aircraft lighting bus is used by the KC 140 to control the intensity
of its panel backlighting. Based on the ratio of the voltage on the Dimbus and the Aircraft voltage,
the KC 140 processor puts out a pulse width modulated output to drive the bulbs in the bezel. The
higher the dimbus voltage ratio, the greater the duty cycle of the PWM signal. The Dimbus voltage
level can be checked on the ANALOG VOLTAGE INPUTS diagnostics page. In addition to the
dimbus voltage, the potentiometer on the front of the bezel can adjust the backlighting brightness
curve.
Revision 2, Dec/2002
CS:15574F02.IDU
BENDIX/KING
KAP 140
DESCRIPTION
AP_DISC
CWS
TRIM_UP
TRIM_ARM
TRIM_DN
STALL_WARNING
DESCRIPTION
DIMBUS
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