Keysight Technologies N3301A Operating instructions

Programming Guide
Keysight DC
Electronic Loads
Models N3300A, N3301A, N3302A, N3303A
N3304A, N3305A, N3306A, and N3307A

Safety Summary
The beginning of the electronic load User’s Guide has a Safety Summary page. Be sure you are familiar
with the information on this page before programming the electronic load from a controller.
Printing History
The edition and current revision of this manual are indicated below. Reprints of this manual containing
minor corrections and updates may have the same printing date. Revised editions are identified by a new
printing date. A revised edition incorporates all new or corrected material since the previous printing
date. Changes to the manual occurring between revisions are covered by change sheets shipped with
the manual.
This document contains proprietary information protected by copyright. All rights are reserved. No part of
this document may be photocopied, reproduced, or translated into another language without the prior
consent of Keysight Technologies. The information contained in this document is subject to change
without notice.
Edition 1 _________August 2000
Update1 _________November 2000
Edition 2 _________March 2002
Edition 3 _________November 2014
4

Table of Contents
Safety Summary 4
Printing History 4
Table of Contents 5
1 - GENERAL INFORMATION 11
About this Guide 11
Documentation Summary 11
External References 11
SCPI References 11
GPIB References 12
VXIplug&play Power Products Instrument Drivers 12
Supported Applications 12
System Requirements 12
Downloading and Installing the Driver 12
Accessing Online Help 13
2 - INTRODUCTION TO PROGRAMMING 15
GPIB Capabilities of the Electronic Load 15
GPIB Address 15
RS-232 Capabilities of the Electronic Load 16
RS-232 Data Format 16
RS-232 Flow Control 16
Introduction to SCPI 17
Conventions Used in This Guide 17
Types of SCPI Commands 17
Multiple Commands in a Message 18
Moving Among Subsystems 18
Including Common Commands 18
Using Queries 19
Types of SCPI Messages 19
The Message Unit 19
Headers 19
Query Indicator 20
Message Unit Separator 20
Root Specifier 20
Message Terminator 20
SCPI Data Formats 20
Numerical Data Formats 20
5

Suffixes and Multipliers 21
Response Data Types 21
SCPI Command Completion 21
Using Device Clear 22
RS-232 Troubleshooting 22
SCPI Conformance Information 23
SCPI Conformed Commands 23
Non-SCPI Commands 23
3 - PROGRAMMING EXAMPLES 25
Introduction 25
Programming the Input 25
Power-on Initialization 25
Enabling the Input 25
Input Voltage 25
Input Current 26
Setting the Triggered Voltage or Current Levels 26
Programming Transients 27
Continuous Transients 27
Pulse Transients 27
Toggled Transients 28
Programming Lists 28
Programming Lists for Multiple Channels 30
Triggering Transients and Lists 31
SCPI Triggering Nomenclature 31
List Trigger Model 31
Initiating List Triggers 32
Specifying a Trigger Delay 32
Generating Transient and List Triggers 32
Making Measurements 33
Voltage and Current Measurements 33
Triggering Measurements 35
SCPI Triggering Nomenclature 35
Measurement Trigger Model 35
Initiating the Measurement Trigger System 36
Generating Measurement Triggers 36
Controlling Measurement Samples 37
Varying the Sampling Rate 37
Measurement Delay 37
Multiple Measurements 37
Synchronizing Transients and Measurements 38
6

Measuring Triggered Transients or Lists 38
Measuring Dwell-Paced Lists 39
Programming the Status Registers 40
Power-On Conditions 43
Channel Status Group 43
Channel Summary Group 43
Questionable Status Group 43
Standard Event Status Group 43
Operation Status Group 44
Status Byte Register 44
Determining the Cause of a Service Interrupt 45
Servicing Standard Event Status and Questionable Status Events 45
Programming Examples 46
CC Mode Example 46
CV Mode Example 46
CR Mode Example 47
Continuous Transient Operation Example 47
Pulsed Transient Operation Example 48
Synchronous Toggled Transient Operation Example 48
Battery Testing Example 49
Power Supply Testing Example 51
C++ Programming Example 52
4 - LANGUAGE DICTIONARY 55
Introduction 55
Subsystem Commands 55
Common Commands 56
Programming Parameters 56
Calibration Commands 57
CALibrate:DATA 57
CALibrate:IMON:LEVel 57
CALibrate:IPR:LEVel 57
CALibrate:LEVel 57
CALibrate:PASSword 58
CALibrate:SAVE 58
CALibrate:STATe 58
Channel Commands 59
CHANnel INSTrument 59
Input Commands 60
[SOURce:]INPut [SOURce:]OUTPut 60
[SOURce:]INPut:PROTection:CLEar [SOURce:]OUTput:PROTection:CLEar 60
[SOURce:]INPut:SHORt [SOURce:]OUTPut:SHORt 60
[SOURce:]CURRent 61
[SOURce:]CURRent:MODE 61
[SOURce:]CURRent:PROTection 61
[SOURce:]CURRent:PROTection:DELay 62
[SOURce:]CURRent:PROTection:STATe 62
[SOURce:]CURRent:RANGe 62
7

[SOURce:]CURRent:SLEW 63
[SOURce:]CURRent:SLEW:NEGative 63
[SOURce:]CURRent:SLEW:POSitive 63
[SOURce:]CURRent:TLEVel 64
[SOURce:]CURRent:TRIGgered 64
[SOURce:]FUNCtion [SOURce:]MODE 64
[SOURce:]FUNCtion:MODE 65
[SOURce:]RESistance 65
[SOURce:]RESistance:MODE 65
[SOURce:]RESistance:RANGe 66
[SOURce:]RESistance:SLEW 66
[SOURce:]RESistance:SLEW:NEGative 66
[SOURce:]RESistance:SLEW:POSitive 67
[SOURce:]RESistance:TLEVel 67
[SOURce:]RESistance:TRIGgered 67
[SOURce:]VOLTage 68
[SOURce:]VOLTage:MODE 68
[SOURce:]VOLTage:RANGe 68
[SOURce:]VOLTage:SLEW 69
[SOURce:]VOLTage:SLEW:NEGative 69
[SOURce:]VOLTage:SLEW:POSitive 70
[SOURce:]VOLTage:TLEVel 70
[SOURce:]VOLTage:TRIGgered 70
Measurement Commands 71
ABORt 71
MEASure:ARRay:CURRent? FETCh:ARRay:CURRent? 71
MEASure:ARRay:POWer? FETCh:ARRay:POWer? 71
MEASure:ARRay:VOLTage? FETCh:ARRay:VOLTage? 72
MEASure:CURRent? FETCh:CURRent? 72
MEASure:CURRent:ACDC? FETCh:CURRent:ACDC? 72
MEASure:CURRent:MAXimum? FETCh:CURRent:MAXimum? 72
MEASure:CURRent:MINimum? FETCh:CURRent:MINimum? 73
MEASure:POWer? FETCh:POWer? 73
MEASure:POWer:MAXimum? FETCh:POWer:MAXimum? 73
MEASure:POWer:MINimum? FETCh:POWer:MINimum? 73
MEASure:VOLTage? FETCh:VOLTage? 74
MEASure:VOLTage:ACDC? FETCh:VOLTage:ACDC? 74
MEASure:VOLTage:MAXimum? FETCh:VOLTage:MAXimum? 74
MEASure:VOLTage:MINimum? FETCh:VOLTage:MINimum? 74
SENSe:CURRent:RANGe 75
SENSe:SWEep:POINts 75
SENSe:SWEep:OFFSet 75
SENSe:SWEep:TINTerval 76
SENSe:WINDow 76
SENSe:VOLTage:RANGe 76
Port Commands 77
PORT0 77
PORT1 77
List Commands 78
[SOURce:]LIST:COUNt 78
[SOURce:]LIST:CURRent [SOURce:]LIST:CURRent:POINts? 78
[SOURce:]LIST:CURRent:RANGe [SOURce:]LIST:CURRent:RANGe:POINts? 79
8

[SOURce:]LIST:CURRent:SLEW [SOURce:]LIST:CURRent:SLEW:POINts? 79
[SOURce:]LIST:CURRent:SLEW:NEGative 80
[SOURce:]LIST:CURRent:SLEW:POSitive 80
[SOURce:]LIST:CURRent:TLEVel [SOURce:]LIST:CURRent:TLEVel:POINts? 80
[SOURce:]LIST:FUNCtion [SOURce:]LIST:MODE [SOURce:]LIST:FUNCtion:POINTs? 81
[SOURce:]LIST:DWELl [SOURce:]LIST:DWELl:POINts? 81
[SOURce:]LIST:RESistance [SOURce:]LIST:RESistance:POINts? 82
[SOURce:]LIST:RESistance:RANGe [SOURce:]LIST:RESistance:RANGe:POINts? 82
[SOURce:]LIST:RESistance:SLEW [SOURce:]LIST:RESistance:SLEW:POINts? 83
[SOURce:]LIST:RESistance:SLEW:NEGative 83
[SOURce:]LIST:RESistance:SLEW:POSitive 83
[SOURce:]LIST:RESistance:TLEVel [SOURce:]LIST:RESistance:TLEVel:POINTs? 84
[SOURce:]LIST:STEP 84
[SOURce:]LIST:TRANsient [SOURce:]LIST:TRANsient:POINts? 84
[SOURce:]LIST:TRANsient:DCYCle [SOURce:]LIST:TRANsient:DCYCle:POINts? 85
[SOURce:]LIST:TRANsient:FREQuency [SOURce:]LIST:TRANsient:FREQuency:POINts? 85
[SOURce:]LIST:TRANsient:MODE [SOURce:]LIST:TRANsient:MODE:POINts? 85
[SOURce:]LIST:TRANsient:TWIDth [SOURce:]LIST:TRANsient:TWIDth:POINts? 86
[SOURce:]LIST:VOLTage [SOURce:]LIST:VOLTage:POINts? 86
[SOURce:]LIST:VOLTage:RANGe [SOURce:]LIST:VOLTage:RANGe:POINTs? 86
[SOURce:]LIST:VOLTage:SLEW [SOURce:]LIST:VOLTage:SLEW:POINts? 87
[SOURce:]LIST:VOLTage:SLEW:NEGative 87
[SOURce:]LIST:VOLTage:SLEW:POSitive 88
[SOURce:]LIST:VOLTage:TLEVel [SOURce:]LIST:VOLTage:TLEVel:POINts? 88
Transient Commands 89
[SOURce:]TRANsient 89
[SOURce:]TRANsient:DCYCle 89
[SOURce:]TRANsient:FREQuency 89
[SOURce:]TRANsient:MODE 90
[SOURce:]TRANsient:LMODE 90
[SOURce:]TRANsient:TWIDth 90
Status Commands 91
Bit Configuration of Channel Status Registers 91
STATus:CHANnel? 91
STATus:CHANnel:CONDition? 91
STATus:CHANnel:ENABle 91
STATus:CSUM? 92
STATus:CSUMmary:ENABle 92
Bit Configuration of Operation Status Registers 92
STATus:OPERation? 92
STATus:OPERation:CONDition? 92
STATus:OPERation:ENABle 93
STATus:OPERation:NTRansition STATus:OPERation:PTRansition 93
Bit Configuration of Questionable Status Registers 94
STATus:QUEStionable? 94
STATus:QUEStionable:CONDition? 94
STATus:QUEStionable:ENABle 94
System Commands 95
SYSTem:ERRor? 95
SYSTem:LOCal 95
SYSTem:REMote 95
SYSTem:RWLock 95
9

SYSTem:VERSion? 95
Trigger Commands 96
ABORt 96
INITiate:SEQuence INITiate:NAME 96
INITiate:SEQuence2 INITiate:NAME 96
INITiate:CONTinuous:SEQuence INITiate:CONTinuous:NAME 97
TRIGger 97
TRIGger:DELay 97
TRIGger:SEQuence2:COUNt 98
TRIGger:SOURce 98
TRIGger:TIMer 98
Common Commands 99
*CLS 99
*ESE 99
Bit Configuration of Standard Event Status Enable Register 100
*ESR? 100
*IDN? 100
*OPC 100
*OPT? 101
*PSC 101
*RCL 101
*RDT? 102
*RST 102
*SAV 103
*SRE 103
*STB? 103
Bit Configuration of Status Byte Register 104
*TRG 104
*TST? 104
*WAI 104
A - SCPI COMMAND TREE 105
Command Syntax 105
B - ERROR MESSAGES 109
Error Number List 109
C - COMPARING N3300A ELECTRONIC LOADS WITH EARLIER MODELS 113
Introduction 113
INDEX 117
10

1
General Information
About this Guide
This manual contains programming information for the Keysight Technologies N3301A, N3302A,
N3303A, N3304A, N3305A, N3306A, and N3307A Electronic Load modules when installed in a Keysight
Technologies N3300A and N3301A Electronic Load mainframes. These units will be referred to as
"electronic load" throughout this manual. You will find the following information in the rest of this guide:
Chapter 1
Introduction to this guide.
Chapter 2
Introduction to SCPI messages structure, syntax, and data formats.
Chapter 3
Introduction to programming the electronic load with SCPI commands.
Chapter 4
Dictionary of SCPI commands.
Appendix A
SCPI command tree.
Appendix B
Error messages
Appendix C
Comparison With Earlier Models
Documentation Summary
The following documents that are related to this Programming Guide have additional helpful information
for using the electronic load.
 Quick Start Guide - located in the front part of the User's Guide. Information on how to quickly get
started using the electronic load.
 User's Guide. Includes specifications and supplemental characteristics, how to use the front
panel, how to connect to the instrument, and calibration procedures.
External References
SCPI References
The following documents will assist you with programming in SCPI:
 Standard Commands for Programmable Instruments Volume 1, Syntax and Style
 Standard Commands for Programmable Instruments Volume 2, Command References
 Standard Commands for Programmable Instruments Volume 3, Data Interchange Format
 Standard Commands for Programmable Instruments Volume 4, Instrument Classes
To obtain a copy of the above documents, contact: Fred Bode, Executive Director, SCPI Consortium,
8380 Hercules Drive, Suite P3, Ls Mesa, CA 91942, USA
11

1 - General Information
GPIB References
The most important GPIB documents are your controller programming manuals - GW BASIC, GPIB
Command Library for MS DOS, etc. Refer to these for all non-SCPI commands (for example: Local
Lockout).
The following are two formal documents concerning the GPIB interface:
 ANSI/IEEE Std. 488.1-1987 IEEE Standard Digital Interface for Programmable Instrumentation.
Defines the technical details of the GPIB interface. While much of the information is beyond the
need of most programmers, it can serve to clarify terms used in this guide and in related
documents.
 ANSI/IEEE Std. 488.2-1987 IEEE Standard Codes, Formats, Protocols, and Common
Commands. Recommended as a reference only if you intend to do fairly sophisticated
programming. Helpful for finding precise definitions of certain types of SCPI message formats,
data types, or common commands.
The above two documents are available from the IEEE (Institute of Electrical and Electronics Engineers),
345 East 47th Street, New York, NY 10017, USA.
VXIplug&play Power Products Instrument Drivers
VXIplug&play instrument drivers for Microsoft Windows 95 and Windows NT are now available on the
Web at http://www.keysight.com/find/drivers. These instrument drivers provide a high-level
programming interface to your Keysight Technologies electronic load. VXIplug&play instrument drivers
are an alternative to programming your instrument with SCPI command strings. Because the instrument
driver's function calls work together on top of the VISA I/O library, a single instrument driver can be
used with multiple application environments.
Supported Applications
 Keysight VEE
 Microsoft Visual BASIC
 Microsoft Visual C/C++
 Borland C/C++
 National Instruments LabVIEW
 National Instruments LabWindows/CVI
System Requirements
The VXIplug&play instrument driver complies with the following:
 Microsoft Windows 95
 Microsoft Windows NT 4.0
 HP VISA revision F.01.02
 National Instruments VISA 1.1
Downloading and Installing the Driver
NOTE: Before installing the VXIplug&play instrument driver, make sure that you have one of the
supported applications installed and running on your computer.
12

General Information - 1
1. Access Keysight Technologies Web site at http://www.keysight.com/find/drivers.
2. Select the instrument for which you need the driver.
3. Click on the driver, either Windows 95 or Windows NT, and download the executable file to your
PC.
4. Locate the file that you downloaded from the Web. From the Start menu select Run
<path>:\kexxxx.exe - where <path> is the directory path where the file is located, and kexxxx is
the instrument driver that you downloaded.
5. Follow the directions on the screen to install the software. The default installation selections will
work in most cases. The readme.txt file contains product updates or corrections that are not
documented in the on-line help. If you decide to install this file, use any text editor to open and
read it.
6. To use the VXIplug&play instrument driver, follow the directions in the VXIplug&play online help
for your specific driver under “Introduction to Programming”.
Accessing Online Help
A comprehensive online programming reference is provided with the driver. It describes how to get
started using the instrument driver with Keysight VEE, LabVIEW, and LabWindows. It includes
complete descriptions of all function calls as well as example programs in C/C++ and Visual BASIC.
 To access the online help when you have chosen the default Vxipnp start folder, click on the Start
button and select Programs | Vxipnp | Kexxxx Help (32-bit).
- where Kexxxx is the instrument driver.
13

2
Introduction to Programming
GPIB Capabilities of the Electronic Load
All electronic load functions except for setting the GPIB address are programmable over the GPIB. The
IEEE 488.2 capabilities of the electronic load are described in Table 2-1. Refer to Appendix A of your
User's Guide for its exact capabilities.
Table 2-1. IEEE 488 Capabilities of Electronic Loads
GPIB Capabilities
Response
Interface
Function
Talker/Listener
All electronic load functions except for setting the GPIB address are
programmable over the GPIB. The electronic load can send and
receive messages over the GPIB. Status information is sent using a
serial poll. Front panel annunciators indicate the present GPIB state
of the electronic load.
AH1, SH1,
T6. L4
Service Request
The electronic load sets the SRQ line true if there is an enabled
service request condition. Refer to Chapter 3 - Status Reporting for
more information.
SR1
Remote/Local
In local mode, the electronic load is controlled from the front panel
but will also execute commands sent over the GPIB. The electronic
load powers up in local mode and remains in local mode until it
receives a command over the GPIB. Once the electronic load is in
remote mode the front panel RMT annunciator is on, all front panel
keys (except ) are disabled, and the display is in normal
metering mode. Pressing on the front panel returns the
electronic load to local mode. can be disabled using local
lockout so that only the controller or the power switch can return the
electronic load to local mode.
RL1
Device Trigger
The electronic load will respond to the device trigger function.
DT1
Group Execute
Trigger
The electronic load will respond to the group execute trigger
function.
GET
Device Clear
The electronic load responds to the Device Clear (DCL) and
Selected Device Clear (SDC) interface commands. They cause the
electronic load to clear any activity that would prevent it from
receiving and executing a new command (including *WAI and
*OPC?). DCL and SDC do not change any programmed settings.
DCL, SDC
GPIB Address
The electronic load operates from a GPIB address that is set from the front panel. To set the GPIB
address, press the Address key on the front panel and enter the address using the Entry keys. The
address can be set from 0 to 30. The GPIB address is stored in non-volatile memory.
15

2 - Introduction to Programming
RS-232 Capabilities of the Electronic Load
The electronic load provides an RS-232 programming interface, which is activated by commands located
under the front panel Address key. All SCPI commands are available through RS-232 programming.
When the RS-232 interface is selected, the GPIB interface is disabled.
The EIA RS-232 Standard defines the interconnections between Data Terminal Equipment (DTE) and
Data Communications Equipment (DCE). The electronic load is designed to be a DTE. It can be
connected to another DTE such as a PC COM port through a null modem cable.
NOTE: The RS-232 settings in your program must match the settings specified in the front panel
Address menu. Press the front panel Address key if you need to change the settings.
RS-232 Data Format
The RS-232 data is a 10-bit word with one start bit and one stop bit. The number of start and stop bits is
not programmable. However, the following parity options are selectable using the front panel Address
key:
EVEN
Seven data bits with even parity
ODD
Seven data bits with odd parity
MARK
Seven data bits with mark parity (parity is always true)
SPACE
Seven data bits with space parity (parity is always false)
NONE
Eight data bits without parity
Parity options are stored in non-volatile memory.
Baud Rate
The front panel Address key lets you select one of the following baud rates, which is stored in non-volatile
memory:
300 600 1200 2400 4800 9600
RS-232 Flow Control
The RS-232 interface supports the following flow control options that are selected using the front panel
Address key. For each case, the electronic load will send a maximum of five characters after holdoff is
asserted by the controller. The electronic load is capable of receiving as many as fifteen additional
characters after it asserts holdoff.
RTS-CTS
The electronic load asserts its Request to Send (RTS) line to signal hold-off
when its input buffer is almost full, and it interprets its Clear to Send (CTS)
line as a hold-off signal from the controller.
NONE
There is no flow control.
Flow control options are stored in non-volatile memory.
16

Introduction to Programming - 2
Introduction to SCPI
SCPI (Standard Commands for Programmable Instruments) is a programming language for controlling
instrument functions over the GPIB and RS-232 interface. SCPI is layered on top of the hardware-portion
of IEEE 488.2. The same SCPI commands and parameters control the same functions in different
classes of instruments.
Conventions Used in This Guide
Angle brackets < > Items within angle brackets are parameter abbreviations. For example,
<NR1> indicates a specific form of numerical data.
Vertical bar | Vertical bars separate alternative parameters. For example, NORM | TEXT
indicates that either "TEXT" or "NORM" can be used as a parameter.
Square Brackets [ ] Items within square brackets are optional. The representation [SOURce:].
VOLTage means that SOURce: may be omitted.
Braces { } Braces indicate parameters that may be repeated zero or more times. It is
used especially for showing arrays. The notation <A>{<,B>} shows that
parameter "A" must be entered, while parameter "B" may be omitted or
may be entered one or more times.
Computer font Computer font is used to show program lines in text.
OUTPUT 723 "TRIGger:COUNt:CURRent 10" shows a program line.
Types of SCPI Commands
SCPI has two types of commands, common and subsystem.
♦ Common commands generally are not related to specific operation but to controlling overall
electronic load functions, such as reset, status, and synchronization. All common commands
consist of a three-letter mnemonic preceded by an asterisk: *RST *IDN? *SRE 8
♦ Subsystem commands perform specific electronic load functions. They are organized into an
inverted tree structure with the "root" at the top. 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.
:CURRent [:LEVel]
:MODE
:PROTection
ROOT
:DELay
:STATus
:CONDition?
:OPERation [:EVENt]?
[:LEVel]
[:IMMediate]
Figure 2-1. Partial Command Tree
17

2 - Introduction to Programming
Multiple Commands in a Message
Multiple SCPI commands can be combined and sent as a single message with one message terminator.
There are two important considerations when sending several commands within a single message:
♦ Use a semicolon to separate commands within a message.
♦ There is an implied header path that affects how commands are interpreted by the electronic
load.
The header path can be thought of as a string that gets inserted before each command within a
message. For the first command in a message, the header path is a null string. For each subsequent
command the header path is defined as the characters that make up the headers of the previous
command in the message up to and including the last colon separator. An example of a message with
two commands is:
CURR:LEV 3;PROT:STAT OFF
which shows the use of the semicolon separating the two commands, and also illustrates the header path
concept. Note that with the second command, the leading header "CURR" was omitted because after the
"CURR:LEV 3" command, the header path became defined as "CURR" and thus the instrument
interpreted the second command as:
CURR:PROT:STAT OFF
In fact, it would have been syntactically incorrect to include the "CURR" explicitly in the second
command, since the result after combining it with the header path would be:
CURR:CURR:PROT:STAT OFF
which is incorrect.
Moving Among Subsystems
In order to combine commands from different subsystems, you need to be able to reset the header path
to a null string within a message. You do this by beginning the command with a colon (:), which discards
any previous header path. For example, you could clear the output protection and check the status of the
Operation Condition register in one message by using a root specifier as follows:
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 20;PROTection 28; :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 subsystems.
Including Common Commands
You can combine common commands with subsystem commands in the same message. Treat the
common command as a message unit by separating it with a semicolon (the message unit separator).
Common commands do not affect the header path; you may insert them anywhere in the message.
VOLTage:TRIGgered 17.5;:INITialize;*TRG
OUTPut OFF;*RCL 2;OUTPut ON
18

Introduction to Programming - 2
Using Queries
Observe the following precautions with queries:
♦ Set up the proper number of variables for the returned data. For example, if you are reading back
a measurement array, you must dimension the array according to the number of measurements
that you have placed in the measurement buffer.
♦ Read back all the results of a query before sending another command to the electronic load.
Otherwise a Query Interrupted error will occur and the unreturned data will be lost.
Types of SCPI Messages
There are two types of SCPI messages, program and response.
♦ A program message consists of one or more properly formatted SCPI commands sent from the
controller to the electronic load. The message, which may be sent at any time, requests the
electronic load to perform some action.
♦ A response message consists of data in a specific SCPI format sent from the electronic load to
the controller. The electronic load sends the message only when commanded by a program
message called a "query."
The following figure illustrates SCPI message structure:
Data
Headers
Header Separator
Message Unit Separators
Message Unit
Query Indicator
Message Terminator
Root Specifier
<NL>VOLT:LEV 20 TLEV 30
;; : CURR?
Figure 2-2. Command Message Structure
The Message Unit
The simplest SCPI command is a single message unit consisting of a command header (or keyword)
followed by a message terminator. The message unit may include a parameter after the header. The
parameter can be numeric or a string.
ABORt<NL>
VOLTage 20<NL>
Headers
Headers, also referred to as keywords, are instructions recognized by the electronic load. Headers may
be either in the long form or the short form. In the long form, the header is completely spelled out, such as
VOLTAGE, STATUS, and DELAY. In the short form, the header has only the first three or four letters,
such as VOLT, STAT, and DEL.
19

2 - Introduction to Programming
Query Indicator
Following a header with a question mark turns it into a query (VOLTage?, VOLTage:PROTection?). If a
query contains a parameter, place the query indicator at the end of the last header
(VOLTage:PROTection? MAX).
Message Unit Separator
When two or more message units are combined into a compound message, separate the units with a
semicolon (STATus:OPERation?;QUEStionable?).
Root Specifier
When it precedes the first header of a message unit, the colon becomes the root specifier. It tells the
command parser that this is the root or the top node of the command tree.
Message Terminator
A terminator informs SCPI that it has reached the end of a message. Three permitted messages
terminators are:
♦ newline (<NL>), which is ASCII decimal 10 or hex 0A.
♦ end or identify (<END>)
♦ both of the above (<NL><END>).
In the examples of this guide, there is an assumed message terminator at the end of each message.
NOTE: All RS-232 response data sent by the electronic load is terminated by the ASCII
character pair <carriage return><newline>. This differs from GPIB response data which is
terminated by the single character <newline> with EOI asserted.
SCPI Data Formats
All data programmed to or returned from the electronic load is ASCII. The data may be numerical or
character string.
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
<NR2>
Digits with an explicit decimal point. Example: .0273
<NR3>
Digits with an explicit decimal point and an exponent. Example: 2.73E+2
Listening Formats
<Nrf>
Extended format that includes <NR1>, <NR2> and <NR3>. Examples: 273 273. 2.73E2
<Nrf+>
Expanded decimal format that includes <NRf> and MIN MAX. Examples: 273 273.
2.73E2 MAX. MIN and MAX are the minimum and maximum limit values that are
implicit in the range specification for the parameter.
<Bool>
Boolean Data. Example: 0 | 1 or ON | OFF
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