HP 8340B Manual page 270

Front Panel
Theory of Operation
FRONT PANEL MICROPROCESSOR
The
front panel assembly contains a
microprocessor that is used to refresh the displays. The main
instrument microprocessor sends data to the front panel processor
via
the instrument data bus and
instrument address
bus. The front panel processor stores the data in
an internal
RAM (random
access memory) buffer. The front panel processor
has
2K of internal ROM (read only memory) that
contains
a
program to generate the necessary control signals to display and refresh data.
DISPLAYS
The synthesizer has two types of displays:
•
Entry display
Includes twenty-eight
5 X 7
dot matrix characters, and
can display both alpha and
numeric
data.
• Frequency and power
displays
Seven-segment displays that usually display only
numeric data.
The
front panel processor determines
the
segments and/or
dots to be illuminated and outputs the
appropriate digital signals to the appropriate circuitry, continually refreshing
the displays.
LED ANNUNCIATORS
The
main instrument microprocessor controls the LED annunciators via the instrument data bus and
instrument address bus.
KEYBOARDS
The two
keyboard assemblies (A5 and
A7), and
the RPG (rotary pulse generator) communicate with
the
main instrument microprocessor
via the A6 keyboard interface assembly. Pressing
a
key gener¬
ates an active low column signal and an active low
row
signal
that are encoded by the keyboard
interface assembly.
A
service request is
generated to
the main instrument microprocessor, which
reads the encoded signal via the instrument data
bus.
G
-2 Front Panel Theory of Operation
HP 8340B/41B