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Eliminating Common SCPI Errors Roger Chaplin
May 17, 1993
There are three SCPI errors which occur more often than any others:
-113, "Undefined header"
-410, "Query INTERRUPTED"
-420, "Query UNTERMINATED"
This paper gives likely causes for these errors, and ideas for avoiding
them.
-113, "Undefined header"
------------------------
This error indicates that what you sent to the instrument did not
contain a recognizable command name. The most likely causes for this
are:
1. Missing space between the command and its parameter. There
must be one or more spaces (blanks) between the command and its
parameter. For example:
:sens:volt:dc:rang100 wrong
:sens:volt:dc:rang 100 right
2. Improper short or long form. Check the manual or the Quick
Reference Guide for the correct command name.
3. Blanks (spaces) within the command name. Blanks are not
permitted within the command name. For example:
:syst:err? right
:syst: err? wrong
-410, "Query INTERRUPTED"
-------------------------
This error occurs when you have sent a valid query to the instrument,
then send it another command or query, or a Group Execute Trigger (GET)
before it has had a chance to send the entire response message
(including the line-feed/EOI terminator). The most likely causes are:
1. Sending a query to the instrument and then sending another
command or query before reading the response to the first query. For
example, the following sequence of commands will cause an error -410:
send syst:err?
send *opc?
because you must read the response to syst:err? before sending another
command or query.
2. Incorrectly configured IEEE 488 driver. The driver must be
configured so that when talking on the bus it sends line-feed with EOI
as the terminator, and when listening on the bus it expects line-feed
with EOI as the terminator. See the reference manual for your
particular IEEE 488 interface.
-420, "Query UNTERMINATED"
--------------------------
This error occurs when you addess the instrument to talk and it has
nothing to say. The most likely causes are:
1. Not sending a query. You must send a valid query to the
instrument before addressing it to talk. This is true even of
measuring instruments, such as the Model 2001. You cannot get a
reading from the 2001 until you send it a query.
2. Sending an invalid query. If you have sent a query and still
get this error, make sure that the instrument is processing the query
without error. For example, sending an ill-formed query which
generates an error -113, "Undefined header" and then addressing the
instrument to talk will generate an error -420, "Query UNTERMINATED" as
well.
3. Valid query following an invalid command. This can occur when
you send mutiple commands or queries (program message units) within one
command string (program message). When the Model 2001 detects an error
in a program message unit, it discards all further program message
units until the end of the string. For example, in the following
program message:
:sens:date?;:sens:func?
the first program message unit :sens:date? will generate error -113,
"Undefined header", and the Model 2001 will discard the second program
message unit :sens:func? even though it is a valid query. NOTE: There
are plans to modify the behavior of our SCPI instruments, such that
queries following an erroneous program message unit do not get
discarded, but commands do. This feature will be listed in the release
notes for existing products when new firmware contains this
modification, and in the User Manual for new products.