With data delay, you can phase shift the acquisition channels, generation channels, and the exported clock. By configuring data and clock positions, you can use your NI digital waveform generator/analyzer for many common applications including, measuring setup and hold times, measuring propagation delays, and maximizing the timing margins among high-speed data transfers. Data delay is available only on Synchronization and Memory Core (SMC)-based products. On these products, you can have one data delay value for generation and one for acquisition only. You can also choose to apply a delay for generation or acquisition per-channel.
This feature is especially important for faster digital signals because at higher rates, clock periods get smaller. Because of these smaller clock periods, it is not enough to just sample at rising or falling edges, because the length that the data is valid might not fall on a rising or a falling edge of the clock. Thus, by shifting the clock by a certain value, you can be sure to sample only when the data is valid and eliminate false data, which might be sampled during the setup and hold times.
For example, you can delay your acquisition channels by 1/64 of your clock period, and delay your generation channels by only 1/256 of your clock period.
Figure 1 shows data delay being used with generation. The data delay tDD(Tx), is added to the Clock to Out Time (tCO) to delay the data by the specified amount.
Figure 1. Data Delay (Generation): The clock is shifted so that it is not aligned with the data, thus ensuring that sampling occurs outside of the setup and hold times. This helps with applications where phenomena such as propagation delay might occur.
You can use data delay with acquisition as well. In this case, the sample taken is delayed by tDD(Rx).
Figure 2. Data Delay (Acquisition): You can also use data delay for acquisition of digital signals. The clock can be shifted by a certain amount so that the signal can be sampled in "clean" areas of the digital signal. Using data delay, “bad” sampling, which can be caused by sampling in transition areas, can be prevented.