Agilent Technologies 54621A Programmer's Manual page 11

Introduction to Programming
Program Message Syntax
Instructions
Instructions (both commands and queries) normally appear as a string
embedded in a statement of your host language, such as BASIC, Pascal, or C.
The only time a parameter is not meant to be expressed as a string is when the
instruction's syntax definition specifies <block data>, such as <learn string>.
There are only a few instructions that use block data.
Instructions are composed of two main parts:
• The header, which specifies the command or query to be sent.
• The program data, which provide additional information needed to clarify
the meaning of the instruction.
Instruction Header
The instruction header is one or more mnemonics separated by colons (:) that
represent the operation to be performed by the instrument. The command tree
in chapter 5 illustrates how all the mnemonics can be joined together to form a
complete header (see chapter 5, "Programming and Documentation
Conventions").
The example in Figure 1-1 is a command. Queries are indicated by adding a
question mark (?) to the end of the header. Many instructions can be used as
either commands or queries, depending on whether or not you have included
the question mark. The command and query forms of an instruction usually
have different program data. Many queries do not use any program data.
White Space (Separator)
White space is used to separate the instruction header from the program data.
If the instruction does not require any program data parameters, you do not
need to include any white space. In this manual, white space is defined as one
or more space characters. ASCII defines a space to be character 32 (in decimal).
Program Data
Program data are used to clarify the meaning of the command or query. They
provide necessary information, such as whether a function should be on or off,
or which waveform is to be displayed. Each instruction's syntax definition shows
the program data, as well as the values they accept. The section "Program Data
Syntax Rules" in this chapter has all of the general rules about acceptable values.
When there is more than one data parameter, they are separated by commas(,).
Spaces can be added around the commas to improve readability.
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