Software-timed sequences are a great way to get up and running quickly when automating measurements from an SMU. However, they can wreak havoc on your test system’s determinism when software jitter becomes a factor during time-sensitive sequences. As an added speed advantage, this approach removes the communication latency between the host computer and instrument between each measurement. Hardware-timed sequences allow you to change various parameters of the SMU such as output mode, aperture time, current range, transient response, at each step.
Figure 7. Software-timed sequences (grey) run irregularly compared to the deterministic execution of hardware-timed sequences (blue).
For more information about hardware-timed sequencing, refer to the Measurement and Update Timing Characteristics section of the NI PXIe-4139 Device Specifications. As an added bonus, NI SMUs have the ability to send ‘Source Complete,’ ‘Measure Complete,’ and ‘Sequence Complete’ triggers to other instruments to synchronize measurements in advanced test systems.