Fluke 93 Service Manual page 37

CIRCUIT
DESCRIPTIONS
3
•
5
•
A
multitasking kernel for
hardware and
software scheduling
Processing
the acquiree data
Is
only
one
of
the tasks of the microprocessor.
The
ScopeMeter uses
a multitasking kernel for hardware and
software
schedullrig,
based on
internal
and
external Interrupts.
The
microprocessor contains
Internal timers,
which can
be
programmed
by
the software.
One
of
these timers
is
used
to
generate
interrupts, e.g. to
scan
the keypad for depressed or released keys,
Except processing
(calibrating)
the acquired data, the
microprocessor
also
does mathematical
computatlone and
controls the hardware.
The
multitasking kernel
takes care
that
every
20
ms
of
processing
time,
a
task
is
Interrupted.
This task
will
then be held and rescheduled, unless
it
requires
execution without
Interruption,
kn this
way
a
variety
of
user-requested tasks can be handled
quasi-
si
muttaneously, without the user being
aware
of the
heavy loads
on
the mioroprocsssor. The
display
of
the
data
on
the
LCD
Is
done
by the
Digital
ASIC,
also taking part
in
the multitasking scheme.
*
Sampling and
Triggering
The ScopeMeter
uses two
types of sampling,
commonly
used
in
many
Digital
Storage Oscilloscopes:
REAL-TIME
SAMPLING
and
RANDOM
REPETITIVE SAMPLING.
In
the real-time
sampling
mode
(time base
settings: 60s/div...1 ^s/dlvj the
ScopeMeter
lakes a
series
of
samples from
a
single
period
of
the Input
signal.
These samples
are
later
used
to reconstruct
the
signal. During the
rsa)-t)me
sampling mode,
the
Digital
ASIC
calculates the
trigger
pulses out
of
the
acquired data
(for
timebase
settings
between
60s/dlv...50ps/div). For
timebase
settings
between
20
ps/div
and
1
ps/div.
the triggering
Is
done by
the Analog ASIC, using analog comparators.
In
random
repetitive
sampling
mode,
the
ScopeMeter
takes
a
sample from successive
cycles
in
a
repetitive signal.
These
samples
are stored
In
memory
and combined
to
reconstmet
the
original
signal.
In this
sampling
mode, samples
are
taken from
the input
signal at intervals
determined by the
internal
ScopeMeter
clock.
Since
there
Is
no
time-correlation
between
the
system's
clock
and
the
Incoming
signal,
all
samples
are taken
at
random
points
of
the
signal.
time between
the trigger
moment
and
the
sampling
moment
must be tracked
to
enable
reconstruction of the signal
from the samples.
This
time,
DELTA
T,
Is
generated by
the
Analog ASIC. See
section 3.4.5 and
figure 3.12.
During
random
repetitive
sampling
mode,
the
ScopeMeter
always uses analog
triggering
(Analog
ASIC).