ERROR HANDLING
Errors may be
divided
into three groups
-
foreground errors generally caused by a user,
background errors which represent
a condition of the instrument and GPIB errors
which
occur
only
when
the unit is being controlled by a GPIB controller.
Foreground errors
Attempts to set the instrument to a parameter value
outside its
known
range result in the
generation of
an error message.
For example, trying
to
select
a
carrier
frequency above or below the specified range
results in the message Carrier Outside Limits being displayed at the
top
of the screen.
Foreground errors
are
cleared
automatically when a correct entry is made by the user.
Background errors
An incorrect operating
condition
within the instrument automatically generates
an
error
message to warn the operator. For example,
if
the
internal frequency standard should
fail
the
message hit. Standard Failure
will
be displayed at the top of the screen.
GPIB errors
Errors caused by
incorrect
programming
are
displayed at the top
of the screen
and may
also
generate
a
Service Request if the relevant
status registers are set.
Error display
-
Front panel
Errors
are displayed as a single line of text at the top of the screen. If more than one
error is present an internal priority ordering algorithm determines which
error is
displayed.
Error display
-
GPIB
When an error occurs, its
number is entered into the Error Queue. Errors are not
removed from the queue
when
they are cleared, but only
by
the ERROR? query, which
returns
the error at the head of the
queue,
or
by
the
*CLS command which clears the
whole
queue.
When the queue
contains
an error entry, a bit (<erb>) on the status byte is
set.
The
error queue has a capacity of 100 error numbers. If an error occurs while the queue
is full the last error number is replaced with 255 so that the
ERROR? query returns a
value
of
255 to
indicate a full
queue.
An
empty
queue
returns a value of 0 following an ERROR? query.
In addition to the
error
queue entry, the
appropriate bit in the Standard Event Register
will also be set (one of <cmd>, <exe>, <dde> or <qye>). Many background errors are also
reported in the Hardware and Coupling Status Registers.
For the above registers see Chap.
3-2.
46882-074C
3-1-55
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