3-4
CIRCUIT
DESCRIPTIONS
The power
$upply circuitry Is also
located on the artalog
A2 PCB. The separate Power aPapter/battery
charger PM6907/...
converts
the line voltage Into
15V DC. This voltage
is used by the BATTERY
CHARGER
to Charge a NICad BATTERY
PACK
(PM9086/001
)» if present.
The POWER
SUPPLY section
transforms the input
voltage (fine
operated) or the battery
voltage
(battery
operated) Into
the supply voltages
fjy the various ScopeMeter
circuits
on A1 and A2.
Digital
A1 PCB
The
ScopeMeter Is controlled
by the MICROPROCESSOR
located
on the digital A1 PCB.
This
microprocessor
performs several
control tasks, for
example;
•
Scanning the
KEYPAD for
user commands. The
keypad Is connected
to the microprocessor
via
the KEYPAD
DRIVERS.
-
Communlcatton
with the
outside world via the
OPTICALLY COUPLED
RS-232-C
TRANSCEIVER.
This
section contains
an
Infrared
LED (transmitter)
and a photolranslstor
(receiver).
‘
Monitoring
the battery
voltage (BATTERY
SENSE CIRCUIT).
“
Controlling
the Analog
ASIC on the analog
A2 PCB.
•
Switching
the power
on or
off
(POWER ON/OFF CIRCUIT).
•
Performing
a proper RESET
at power on (RESET
CIRCUIT).
•
Controlling
the analog A2 circuits
(via the ANALOG
CONTOOL
CtRCUfT).
•
SIgnal
p
rocessi
n
g
of acqul red
data . The mlcroproce
ssor reads
,
calibrate
s and stores the
acqu i red
data.
The DIGITAL
ASIC Is the
core of the ScopeMeter's
digital clrcurtry.
It provides:
-
Timebase
functions. For
example: tfte
ScopeMeter's ADC
sampling signal fs generated
by the
Digital ASIC.
•
Trigger functions
(In real-time
sampling mode).
•
Acquisition Control
Logic (ACL).
This function controls
the acquisition
according to trigger
and
acquisition modes.
The Digital ASIC
contains acquisition
RAM for quick
data storage.
Mln/Maxmode.
•
Decoding of the
Internal ASIC addresses
and synchronization
of Digital
ASIC and microprocessor
access to the
acquisition RAM.
•
Display
control. The Digital
ASIC generates the
picture to be
displayed on the LCD.
The picture,
generated by
the
Digital
ASIC is displayed
on the Liquid Crystal Display
(LCD). The
LCD is controlled
by the LCD ROW
DRIVERS and the
LCD COLUMN
DRIVERS. The
LCD SUPPLY
section provides
for the voltages needed,
ScopeMeter
model 97 has a BACKLIGHT
CIRCUIT, which
can illuminate LCD.
3.2.2 Data acquisition
-
Data
acquisition
path in the
ScopeMeter
The analog input signals
are first
attenuated and/or
amplified and then converted
into digital values
by the ADC. The samples
of the Input
signals are stored
in the Acquisition
RAM of the Digital
ASIC.
If
512 samples are stored
in memory, the second
trigger pulse will signal the microprocessor
that the
acquisition Is ready.
(We
assume toatthe
ScopeMeter is using random
repetitive
sampling, see next
section.) Then
the acquired
data is ready for processing.
The microprocessor
reads the
data from the
Acquisition RAM
and processes
the data according
to the actual
calibration values.
These calibration
valuee
(constants) are copied
from Flash
ROM to RAM during
startup. The calibration
values have
been stored in
Flash ROM
during the calibration
process. After
processing, the
data is stored In
the
External
RAMs. These
RAMs also contain
the more static
picture elements, for
example the
grid-,
cursor-
and text data.
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