National Instruments cDAQ-9133 User Manual

Also see for cDAQ-9132: Quick start SAFETY, ENVIRONMENTAL, AND REGULATORY INFORMATION

Contents

National Instruments cDAQ-9133 User Manual Manual pdf 77 page image

4-8 | ni.comChapter 4 Digital Input/Output and PFI• Buffered Change Detection Acquisition—A buffer is a temporary storage in computermemory for acquired samples. In a buffered acquisition, data is stored in the cDAQcontroller onboard FIFO then transferred to a PC buffer. Buffered acquisitions typicallyallow for much faster transfer rates than nonbuffered acquisitions because data accumulatesand is transferred in blocks, rather than one sample at a time.Digital OutputTo generate digital output, insert a digital output C Series module in any slot on the cDAQcontroller. The generation specifications, such as the number of channels, channel configuration,update rate, and output range, are determined by the type of C Series module used. For moreinformation, refer to the documentation included with your C Series module(s).With parallel digital output modules (formerly known as hardware-timed modules), you can domultiple software-timed tasks on a single module, as well as mix hardware-timed andsoftware-timed digital output tasks on a single module. On serial digital output modules,(formerly known as static digital output modules), you cannot mix hardware-timed andsoftware-timed tasks, but you can run multiple software-timed tasks.You may have a hardware-timed task or a software-timed task include channels from multiplemodules, but a hardware-timed task may not include a mix of channels from both parallel andserial modules.Digital Output Data Generation MethodsWhen performing a digital output operation, you either can perform software-timed orhardware-timed generations. Hardware-timed generations must be buffered.Software-Timed GenerationsWith a software-timed generation, software controls the rate at which data is generated. Softwaresends a separate command to the hardware to initiate each digital generation. In NI-DAQmx,software-timed generations are referred to as on-demand timing. Software-timed generations arealso referred to as immediate or static operations. They are typically used for writing out a singlevalue.For software-timed generations, if any DO channel on a serial digital module is used in ahardware-timed task, no channels on that module can be used in a software-timed task.Hardware-Timed GenerationsWith a hardware-timed generation, a digital hardware signal controls the rate of the generation.This signal can be generated internally on the controller or provided externally.Hardware-timed generations have several advantages over software-timed acquisitions:• The time between samples can be much shorter.• The timing between samples is deterministic.• Hardware-timed acquisitions can use hardware triggering.