You can generate digital waveforms on the digital I/O lines. The digital output waveform generation FIFO stores the digital samples.

The USB-6421 has a DMA controller dedicated to moving data from the system memory to the DO waveform generation FIFO. The USB-6421 moves samples from the FIFO to the digital I/O terminals on each rising or falling edge of a clock signal, DO Sample Clock. You can configure each digital I/O signal to be an input, a static output, or a digital waveform generation output.

The FIFO supports a retransmit mode. In the retransmit mode, after all the samples in the FIFO have been clocked out, the FIFO begins outputting all of the samples again in the same order. For example, if the FIFO contains five samples, the pattern generated consists of sample #1, #2, #3, #4, #5, #1, #2, #3, #4, #5, #1, and so on.