© National Instruments Corporation xiii NI USB-621x User ManualAbout This ManualThe NI 621x User Manual contains information about using the NationalInstruments USB-621x data acquisition (DAQ) devices withNI-DAQmx 8.3 and later. NI 621x devices feature up to 32 analog input(AI) channels, up to two analog output (AO) channels, up to eight lines ofdigital input (DI), up to eight lines of digital output (DO), and two counters.ConventionsThe following conventions are used in this manual:<> Angle brackets that contain numbers separated by an ellipsis representa range of values associated with a bit or signal name—for example,AO <3..0>.» The » symbol leads you through nested menu items and dialog box optionsto a final action. The sequence File»Page Setup»Options directs you topull down the File menu, select the Page Setup item, and select Optionsfrom the last dialog box.This icon denotes a note, which alerts you to important information.This icon denotes a caution, which advises you of precautions to take toavoid injury, data loss, or a system crash. When this symbol is marked on aproduct, refer to the Read Me First: Safety and Radio-FrequencyInterference document which can be found at ni.com/manuals, forinformation about precautions to take.bold Bold text denotes items that you must select or click in the software, suchas menu items and dialog box options. Bold text also denotes parameternames.italic Italic text denotes variables, emphasis, a cross-reference, or an introductionto a key concept. Italic text also denotes text that is a placeholder for a wordor value that you must supply.monospace Text in this font denotes text or characters that you should enter from thekeyboard, sections of code, programming examples, and syntax examples.This font is also used for the proper names of disk drives, paths, directories,programs, subprograms, subroutines, device names, functions, operations,variables, filenames, and extensions.
