Operation Model 8901B
Clear Lockout/Set Local
The Modulation Analyzer returns to local operation when
it
receives the Clear Lockout/Set
Local message.
NOTE
Clear LockoutlSet Local can be accomplished
by
switching the power to
STBY
and back to ON. Returning to Local operation in this way has the
following disadvantages:
0
It defeats the purpose of Local Lockout (that
is,
the system controller
will lose control of the Modulation Analyzer).
0
Instrument configuration
is
reset to Power-up conditions listed in the
Detailed Operating Instructions
under “Instrument Preset” on page
3-209.
Service Request Message (SRQ)
The Service Request Message (SRQ message)
is
being issued when the SRQ bus line is asserted and
the SRQ light on the front panel is lit by the instrument. The Service Request message may be issued
under following conditions:
0
the instrument requires re-calibration
or
is
uncalibrated,
0
there has been a Frequency Offset mode change,
0
an enabled limit has been exceeded,
0
an instrument error has occurred,
0
an HP-IB code error has occurred,
0
measurement
data
is
ready to be read.
The Modulation Analyzer uses its Status Byte and the SRQ Mask (Special F’unction
22)
to
determine
whether
or
not to issue a SRQ message. Refer
to
Figure
3-4,
“Issuing
a
Service Request Message”
throughout the following discussion of the Service Request Message, SRQ Mask and the Status Byte.
The Service Request Message
is
asserted when the RQS bit
of
the Status Byte
is
set by the instrument.
The RQS bit is set automatically when one or more
of
the other bits in the Status Byte are set. For
the bits other than the RQS bit of the Status Byte
to
be set, those bits must be enabled by the SRQ
Mask before the instrument condition which will set them occurs.
The instrument can send the Service Request message in either local or remote operation.
Clearing the Service Request Message.
After
the Service Request message has been sent,
it
will
be cleared when the Status Byte
is
cleared which
is
described below under “Status Byte”.
3-26
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