Specifications

Operating Manual SEFRAM 4451
M4451 A00
38
The Program Data represent the values of the parameters being set, for example, the '1US' in the
above examples. Different forms of program data are accepted, depending on the command.
The Program Data types used in the SEFRAM 4451 are as follows:
1. Character program data – This form of data is comprised of a mnemonic made up of
lower - or upper-case alpha characters. As with Program Header mnemonics, some
Character Data mnemonics have short and long forms. Only the short or the long form
may be used.
2. Boolean data – Boolean data indicate that the parameter can take one of two states, ON
or OFF. The parameter may be character type ON or OFF or numeric. A numeric value is
rounded to an integer. A non-zero result is interpreted as 1 (ON), and a zero result as 0
(OFF). Queries return the values 0 or 1.
3. NRf – This is a decimal numeric data type, where
NR1 indicates an integer number,
NR2 indicates a fixed-point real number, and
NR3 indicates a floating-point real number.
All parameters that have associated units accept a suffix, which may be specified using
upper - or lower-case characters. When the suffix is not specified, the numeric value is
accepted in the default units, which are Hertz for frequency, Seconds for time, and Volts
for voltage. To set the period to 1 microsecond we can send one of the following
commands:
:PULS:PER 1E-6 or :PULS:PER 1000NS
The special forms of character data accepted as numbers as defined by SCPI are NOT
accepted by the SEFRAM 4451.
There are two types of Program Message Units: Command Message Units and Query
Message Units. A Query differs from a Command in that the Program Header is
terminated with a question mark ('?'). For example, the period might be queried with the
following query:
:PULS:PER?
Not all Program Message units have query forms, such as STATUS:PRESET, and some
Program Message Units might have only the query form, such as SYSTEM:VERSION?.
The SEFRAM 4451 puts the response to the query into the output queue, from where it
may be read by the controller. The Status Byte MAV bit is set to indicate to the controller
that a response is ready to be read.
4.9.3 SCPI Command Structure
SCPI commands are based on a hierarchical structure. This allows the same instrument-control
header to be used several times for different purposes, providing that the mnemonic occurs in a
unique position in the hierarchy. Each level in the hierarchy is defined as a node. Mnemonics in
the different levels are separated from each other by a colon (':'). The first Program Message
Unit, or command, in a Program Message is always referenced to the root node. Subsequent
commands are referenced to the same level as the previous command.
A Program Message Unit having a colon as its first character causes the reference to return to
the root. This process is defined by IEEE 488, section A.1.1. Consider the following examples:
1. The following command may be used to set the high and low levels of the pulse. Note
that the LOW command is referenced to the command preceding it. The LOW mnemonic
resides at the same node as the HIGH command.
SOURCE:VOLTAGE:HIGH 5V;LOW 2V
2. This command sets the frequency and the high level. The FREQUENCY and
VOLTAGE mnemonics are at the same level.
SOURCE:FREQUENCY 2KHZ;VOLTAGE:HIGH 4V
3. When Program Message Units describe different subsystems, a colon prefix must be used
to reset the command reference to the root. Here the frequency and the output state are
set.