The “common” commands are recognized and acted upon in a similar manner by all instruments that follow the IEEE488.2 standard, whether a
DVM, scope, frequency meter, gaussmeter, etc. These are the syntax rules:
1) A common command always begins with an asterisk character (*) followed by a three or four-character acronym and possibly one
other parameter. For instance, the command to clear the event registers is *CLS.
2) The commands are not case sensitive. For instance, the *CLS, *cls and *cLS commands are identical.
3) If there is a fourth character in the acronym, it will always be a question mark (?) and indicates that information is being requested
from the instrument. For instance, a command to read the model number and manufacturer of the instrument is *IDN?.
4) If a parameter follows a command, it must be separated from the acronym by one space. The parameter is the ASCII representation
of an integer. For instance, if the parameter to be sent is binary 1100, the actual parameter sent would be the two
ASCII characters 12, since binary 1100 = decimal 12. If you were to send the four ASCII characters 1100 it would be interpreted
as decimal 1100 (eleven hundred).
5) A number returned from the instrument is an ASCII representation of a number. For instance, if the instrument returns the ASCII
string 345 the number is decimal 345 (three hundred forty-five), which translates to 159 hex.
6) Multiple commands can be sent in one string. The commands must be separated by semicolons (;). For instance, *CLS;*IDN? first
clears the event registers and then requests model and manufacturer information. If more than one of the commands in the string
requests information from the instrument, the instrument’s response will also have semicolons separating the responses, such as
345;0;10.
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