Agilent Technologies 6814B, 6834B, 6843A The Effect of Optional Headers, Moving Among Subsystems

Introduction to Programming - 2

If you now enter :CLEar, you have reached the end of the command string. The active header path remains at :CLEar. If you wished, you could have entered :CLEar;DELay 20 and it would be accepted as a compound message consisting of:

OUTPut:PROTection:CLEAr and

OUTPut:PROTection:DELay 20.

The entire message would be:

OUTPut:PROTection:CLEar;DELay 20

The message terminator after DELay 20 returns the path to the root.

The Effect of Optional Headers

If a command includes optional headers, the interface assumes they are there. For example, if you enter OUTPut OFF, the interface recognizes it as OUTPut:STATe OFF. This returns the active path to the root (:OUTPut). But if you enter OUTPut:STATe OFF, then the active path remains at :STATe. This allows you to send

OUTPut:STATe OFF;PROTection:CLEar

in one message. If you tried to send

OUTPut OFF;PROTection:CLEar

the header path would return to :OUTPut instead of :PROTection.

The optional header [SOURce] precedes the current, frequency, function, phase, pulse, list, and voltage subsystems. This effectively makes :CURRent, :FREQuency, :FUNCtion, :PHASe, :PULse, :LIST, and :VOLTage root-level commands.

Moving Among Subsystems

In order to combine commands from different subsystems, you need to be able to restore the active path to the root. You do this with the root specifier (:). For example, you could clear the output protection and check the status of the Operation Condition register as follows:

OUTPut:PROTection:CLEAr

STATus:OPERation:CONDition?

Because the root specifier resets the command parser to the root, you can use the root specifier and do the same thing in one message:

OUTPut:PROTection:CLEAr;:STATus:OPERation:CONDition?

The following message shows how to combine commands from different subsystems as well as within the same subsystem:

VOLTage:LEVel 70;PROTection 80;:CURRent:LEVel 3;PROTection:STATe ON

Note the use of the optional header LEVel to maintain the correct path within the voltage and current subsystems and the use of the root specifier to move between subsytems.

NOTE: The "Enhanced Tree Walking Implementation" given in appendix A of the IEEE 488.2 standard is not implemented in the ac source.

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