Honeywell Bendix/King KX 165A Maintenance Manual page 45

BENDIX/KING
Configuration EEPROM, U1001, contains information unique to each unit that is required for nav
and com operation such as channeling, program memories, electronic tuning, and etc.
4.3.5.3 Digital Interfaces to Other Modules
There are digital logic interfaces to other assemblies of KX155A, including the com/nav receiver,
com transmitter, VOR/LOC convertor, glideslope, and the front panel with the display and input
devices. These lines are either discrete logic level controls or synchronous serial data lines.
Many I/O lines to these assemblies are filtered with a 330pF ceramic cap and in some cases fer-
rite beads (lossy inductor) or series resistors.
4.3.5.4 Discrete Interfaces
There are a few discrete logic level inputs to other instruments and equipment on the airplane. All
these inputs are isolated with a 330pF ceramic capacitor, diode and PNP transistor. An optional
Zener clamp can be used for lightning protection per DO-160C. This buffer should be sufficient in
keeping spikes and other harmful transients from damaging digital ICs on board. An example of
this type of interface can be seen at CR1021, R1249, C1223, CR1044, Q1012, R1102, R1406.
These inputs go directly to microprocessor discrete inputs. Analog/power/non-TTL logic outputs
are driven by transistors or FETs and are also optionally zener protected.
4.3.5.5 Analog Interfaces
The HC16 has an 8 channel ADC. However, there are 15 analog voltages to monitor. Therefore,
an analog multiplexer, U1021, is used to select some of the low-speed signals (mostly voltage
monitors).
Signals monitored by the CPU ADC include:
VOR 30Hz FM
FILTERED_NAV_COMPOSITE
FILTERED_GLIDESLOPE_COMPOSITE
VOR/LOC_FILTERED_STATOR_F
VOR/LOC_FILTERED_STATOR_D
COM_VOLUME
NAV_VOLUME
ANALOG_MUX_OUT which is one of the following
PHOTOCELLTEMPERATURE
+5V (through divider)
-200V (through divider)
-12V (through divider)
+9V (through divider)
FILTERED_11-33_VDC_POWER
Volume controls are done by applying a +5V reference across the Com and Nav volume potenti-
ometers on the front panel then reading the wiper voltage with the ADC. The audio volume is then
adjusted using digital potentiometers in the audio circuit controlled through the general serial bus.
Digital potentiometers U1016, U1028, and U1032 also adjust the level of sidetone, intercom,
transmitter power, receiver noise squelch, RF AGC, and etc.
The 68HC16Z1 also has one RS232 port. This port is level-shifted to RS232 logic levels through
a MAX202, U1022, converter and optionally protected by a bidirectional zener. This port can be
used for the KX165A to communicate with other devices, and may be used to update software in
the field.
Page 4-42 15610M00.RCD
KX 165A
Rev 0, Jun/2000