OPERATION
3-1-72
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
Int. 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.
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.
