Table of Contents
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VXI
OPERATING
MODES
42
The
instrument can be operated
via
the
VXI
using
the
'BYTE
AVAILABLE*
and
'BYTE
REQUEST' VXI
commands.
READING OUT DATA
43
The
rate at
which measurements
are
made
is
determined by
the instrument.
The
output
buffer
is
updated
at the
end
of
each
measurement
cycle,
overwriting the previous
measurement
data
if
this
has not been
transferred
to
the
controller.
44
The
transfer of
data
from
the
instrument
to
the
controller
is
triggered
by
the
controller.
The
instrument's output buffer
is
cleared
when
the data
transfer
is
complete.
Problems
arising
from the
differences
between
the
measurement
rate
and data
transfer trigger rate
are
resolved
according
to
the following
protocol:
(1)
If
data
transfer
is
in
progress
at
the
end
of
a
measurement
cycle,
the
updating
of
the
output
buffer
is
delayed.
The
data
transferred
will
relate
to
the
previous
measurement
cycle.
(2)
If
the
data
transfer trigger occurs
during
a
measurement
cycle
and
the output buffer
is
empty, data
transfer
will
be delayed
until the buffer
is
updated, the data
transferred
will
then
relate
to
the
latest
measurement
cycle.
(3)
If
a
measurement
cycle
is
completed
before the
results of
the previous
cycle
have been
transferred
to
the
controller,
the buffer
will
be
updated.
The
data
for
the previous
cycle
will
he overwritten
and
lost.
45
The
rate at
which
measurements
are
made
can
be controlled
in
the following ways:
(1)
The
gate
time
of
the
instrument
(duration of the
measurement
cycle)
can be
controlled
by
choosing
an
appropriate
resolution.
(2)
The
instrument can be
operated
in
the
HOLD
mode.
Single
measurement
cycles
can
be
triggered,
when
required,
by
means
of the
*TRG
or
MEAS?
commands.
(3)
The
instrument
hold
time
can
be
set
by
entering
a value, in seconds, into
the
sample
store
from
the
controller.
46
The format
of
the data
output
is
described in
TABLE
4.5.
CONTROLLING THE INSTRUMENT
47
All the
instruments
functions are controlled
by
means
of
device-dependent
commands,
sent
via
the
bus,
using
the
'BYTE
AVAILABLE' VXI
command.
2151
OPS
A1571/DA
4-13
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