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Query (?)
Commands ending in a query (?) indicate t hat a response is expected from the
instrument. This is usually a measured value or status message. Commands sent
without a query instruct the instrument to perform a function. The instrument will not
output a response without a query command (except in Talk Only mode).
Common Commands (*)
Commands beginning with a “*” are called common commands and have a precise
function as defined by the IEEE-488.2 standard. All instruments behave in an
identical way. These commands are primarily concerned with control, reset, self-test
and status.
Command Syntax
Most command keywords have both a long and short form. The bus controller can
send commands in either form and also in any combination of upper and lower case
characters. Instrument responses, however, are always in the short form, upper case.
If extra, redundant parameters are sent in a parameter list they are simply ignored.
No error is produced.
e.g.
SENSe:FRESistance:RANGe 30OHM,300OHM
{ignored}
In the description of commands that follo ws, various symbols are used for different
features:
<
parameter
>
represents a field name.
< ON|OFF >
the vertical bar indicates OR
[ optional ]
square brackets indicate optional commands or
parameters.
“string”
indicates an ASCII text string.
Data Types
The bus controller can also send data in a range of formats, but the instrument
always responds in a precise format. There are four principal data types;
Numeric Parameters
are decimal numbers which include an optional sign, mantissa,
decimal point and exponent. Engineering suffix units are not accepted.
Discrete Parameters
have limited values e.g. SINGle, INFinite, and like command
keywords they can have long and short forms, upper and lower case.
Boolean Parameters
have a single binary value. The controller can send OFF or 0,
ON or 1, but the instrument response is always 0 or 1.
String Parameters
contain ASCII characters which are placed between a pair of
double quotation marks, i.e. “ “.
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
