HP 437B Service Manual

HP 437B
Service Sheet BD1
8-16
Note
SERVICE
The
microprocessor
controls
the
Power
Meter
by
interpreting
input
instructions
and
issuing
commands.
Specific
instructions
for
the
microprocessor
are
stored
in
ROM.
Data
is
exchanged
between
the
microprocessor
and
the
other
blocks
of
the
Digital
Section
over
the
data
bus
(D0-D7).
The
address
bus
(A0-A15)
is
used
by
the
microprocessor
to
select
either
specific
data
from
the
RAM
or
instructions
from
the
ROM
and
to
provide
address
and
control
information
inputs
to
the
address
and
control
decoder.
—_— heer rere ee ges
The
RAM
contains
the
frequency
vs.
calibration
factor
(sensor
data)
tables,
This
data
is
protected
by
a
battery
(A3BT1).
This
battery
occasionally
needs
replacement.
For
replacement
indications
and
procedure,
see
"Battery
Replacement
Procedure"
in
the
Digital
Board
Check
further
on
in this
section.
The
address
and
control
decoder
interprets
data
from
the
microprocessor
to
create
control
signals
that
enable
other
components
of
the
Digital
Section
to
gain
access
to
the
data
bus.
The
system
clock
generator
supplies
timing
signals
to
various
components
in
the
Digital
Section.
Two 2.0
MHz
timing
signals
are
sent
to
the
microprocessor,
and
one
2.0
MHz
timing
signal
is
sent
to
the
address
and
control
decoder,
the
analog
PIA,
the
analog
timer,
the
keyboard
and
display
PIA,
the LED
data
latch,
and
the
HP-IB
interface.
An
8.0
MHz
signal
from
the
system
clock
generator
is
sent
to
the
analog
timer
and
the
display/keyboard
controller.
The ROM contains permanent instructions that are interpreted and executed
by the microprocessor. The RAM is used by the microprocessor to store
various data such as front panel conditions and the Sensor Data tables. A
battery supplies power to the RAM when the Power Meter is not connected
to the mains power line. This prevents loss of stored data.
When the Power Meter is turned on, the reset circuitry holds the
microprocessor in the reset state for 25 milliseconds to allow the power
supply to reach a steady +5V. If the +5V power supply drops below +4.5V
the reset circuitry will issue a signal to halt the microprocessor.
The analog PIA is an input/output device that allows the microprocessor to
control the components in the Analog Section. Data from the data bus is
transferred by the analog PIA to the Analog Section. This data is sent to the
Analog Section via eleven data lines and two control lines (STRAMP and
NADS).
The service test buffer is a digital multiplexer. Data lines AAO-AA2,
STRAMP, NADS, and NWR control the multiplexer and select one of 8 data
lines ADO-AD7 from the analog PIA. During self-test, the service test buffer
verifies the data and control lines from the Digital Section to the Analog
Section.

HP 437B Specifications

General

Brand	HP
Model	437B
Category	Measuring Instruments
Language	English