Agilent Technologies 6834B, 6814B, 6843A The SCPI Command Tree, The Root Level, Active Header Path

2 - Introduction to Programming

The SCPI Command Tree

As previously explained, the basic SCPI communication method involves sending one or more properly formatted commands from the SCPI command tree to the instrument as program messages. The following figure shows a portion of a subsystem command tree, from which you access the commands located along the various paths (you can see the complete tree in appendix A).

ROOT

:OUTPut	[:STATe]
	:COUPling
	:DFI	[:STATe]
		:SOURce
	:PROTection	:CLEar
		:DELay
:STATus	:OPERation	[:EVEN] ?
		:CONDition?

Figure 2-1. Partial Command Tree

The Root Level

Note the location of the ROOT node at the top of the tree. Commands at the root level are at the top level of the command tree. The SCPI interface is at this location when:

υthe ac source is powered on

υa device clear (DCL) is sent to the ac source

υthe SCPI interface encounters a message terminator

υthe SCPI interface encounters a root specifier

Active Header Path

In order to properly traverse the command tree, you must understand the concept of the active header path. When the ac source is turned on (or under any of the other conditions listed above), the active path is at the root. That means the SCPI interface is ready to accept any command at the root level, such as OUTPut or STATe.

If you enter OUTPut, the active header path moves one colon to the right . The interface is now ready to accept :STATe, :COUPling, :DFI, or :PROTection as the next header. You must include the colon, because it is required between headers.

If you now enter :PROTection, the active path again moves one colon to the right. The interface is now ready to accept either :CLEar or :DELay as the next header.

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