Agilent Technologies 669xA, 665xA Including Common Commands, SCPI Queries, Value Coupling, Symbol

Note The SCPI parser traverses the command tree as described in Appendix A of the IEEE 488.2 standard. The "Enhanced Tree Walking Implementation" given in that appendix is not implemented in the power supply.

The following message shows how to combine commands from different subsystems as well as within the same subsystem (see Figure 3-2):

VOLTAGE:LEVEL 7;PROTECTION 8;:CURRENT:LEVEL 50;PROTECTION 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.

Including Common Commands

You can combine common commands with system commands in the same message. Treat the common command as a message unit by separating it with the message unit separator. Common commands do not affect the active header path; you may insert them anywhere in the message.

VOLT:TRIG 7.5;INIT;*TRG

OUTP OFF;*RCL 2;OUTP ON

SCPI Queries

Observe the following precautions with queries:

•Remember to set up the proper number of variables for the returned data.

•Set the program to read back all the results of a query before sending another command to the power supply. Otherwise, a Query Interrupted error will occur and the unreturned data will be lost.

Value Coupling

Value coupling results when a command directed to send one parameter also changes the value of a second parameter. There is no direct coupling among any power supply SCPI commands. However, be aware that until they are programmed, uninitialized trigger levels will assume their corresponding immediate levels. For example, if a power supply is powered up and VOLT:LEV is programmed to 6, then VOLT:LEV:TRIG will also be 6 until you program it to another value. Once you program VOLT:LEV:TRIG to another value, it will remain at that value regardless of how you subsequently reprogram VOLT:LEVEL.

SCPI Data Formats

All data programmed to or returned from the power supply is ASCII. The data may be numerical or character string.

Numerical Data

Table 2-1 and Table 2-2 summarize the numerical formats.

Table 2-1. Numerical Data Formats

Symbol	Data Form
	Talking Formats
<NR1>	Digits with an implied decimal point assumed at the right of the least-significant
	digit. Examples: 273 0273
<NR2>	Digits with an explicit decimal point. Example: 273.	.0273
<NR3>	Digits with an explicit decimal point and an exponent.	Example: 2.73E+2 273.0E-2

14 Remote Programming