16 Sequoia Series
If you now enter :VOLTage, the active path again moves one colon to the right. The interface is now
ready to accept either :RANGe or :LEVel as the next header.
If you now enter :RANGe you have reached the end of the command string. The active header path
remains at :RANGe If you wished, you could have entered :RANGe 166 ;LEVel 115 and it would be
accepted as a compound message consisting of:
SOURce:VOLTage:RANGe 166.
SOURce:VOLTage:LEVel 115.
The entire message would be:
SOURce:VOLTage:RANGe 166;LEVel 115
The message terminator after LEVel 115 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 [SOURCe]:VOLTage 115, the interface recognizes it as [SOURce]:VOLTage:LEVel 115. This
returns the active path to the root (:VOLTage). But if you enter [SOURce]:VOLTage:LEVel 115 then
the active path remains at :LEVel This allows you to send
[SOURce]:VOLTage:LEVel 115;RANGe 166
in one message. If you did not send LEVel you are allowed to send the following command:
[SOURce]:VOLTage 115;FREQuency 60
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 open the output relay
and check the status of the Operation Condition register as follows:
OUTPut:STATe ON
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 on; :STATus:OPERation:CONDition?
The following message shows how to combine commands from different subsystems as well as within
the same subsystem:
VOLTage:RANGe 116;LEVel 115;:CURRent 10;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 subsystems. The "Enhanced Tree
Walking Implementation" given in appendix A of the IEEE 488.2 standard is not implemented in the
power source.
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