Honeywell SPZ-8000 Maintenance Manual page 276

The navigation computer has a database capacity of 1.28 megabytes which
enables loading of data to allow international operation without changing
databases. Also, the computer contains an internal battery that keeps
the
clock and calendar running when power is removed.
The navigation computer provides a lateral steering signal to the DAFCS.
The DAFCS will cause the aircraft to bank according to the lateral
steering signal. The lateral steering signal is proportional to the
calculated distance and angle deviations from the desired lateral course.
Lateral steering mode is a desired track mode.
In addition to providing a lateral steering signal, the navigation
computer also provides vertical navigation (VNAV). The VNAV modes are
VNAV altitude (VALT), VNAV altitude preselect (VASEL), VNAV flight level
change (VFLCH), and VNAV vertical path guidance (VPATH). The vertical
command is proportional to the calculated distance from the desired
vertical path. VNAV allows the pilot to define waypoint altitudes and
descent angles to waypoints and command the DAFCS to pitch the aircraft
and
fly the desired vertical path.
The navigation computer also provides guidance and map information to the
pilot via the navigation display. The navigation computer will output to
the Nav display the positions of 51 waypoints (lateral and vertical), 10
closest Navaids, and 9 closest airport reference points as well as
holding pattern information. The display will include the course line
between the waypoints. The waypoint and course line display will give
the pilot a pictorial view of the waypoints with respect to the weather.
The navigation computer has a multi-microprocessor architecture (Figure
9-2). The primary 16-bit processor has a coprocessor for performing
floating point mathematics. The primary processor (pair) handles all the
navigation and guidance calculations as well as the database manipu-
lations and CDU input/output. The remaining two 16-bit microprocessors
are dedicated to handling the sensor inputs and navigation outputs to the
EFIS and autopilot. The two 1/0 processors communicate to the main
processor through shared random access memory.
The navigation computer digital outputs transmitted over the ASCB are
listed in Table 9-2 for basic data and Table 9-3 for background data.
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