NI PXI-5401/5411/5431
Direct Digital Synthesis Lookup Memory

The NI PXI-5401/5411/5431 uses a 32-bit, high-speed accumulator with a lookup memory and a 12-bit DAC for direct digital synthesis-based waveform generation.

You can use the lookup memory in Direct Digital Synthesis mode only. You cannot use the lookup memory in Arbitrary Waveform Generation mode. You can store one cycle of a repetitive waveform-a sine, triangular, square, or arbitrary wave-in the lookup memory. Then, you can change the frequency of that waveform by sending just one instruction. You can use Direct Digital Synthesis mode for very fine frequency resolution function generation. You can generate sine waves of up to 16 MHz for NI PXI-5401/5411 and 8 MHz for NI PXI-5431 with a frequency resolution of 10.0 mHz. Because this mode uses an accumulator, waveform generation loops back to the beginning of the lookup memory after passing through the end of the lookup memory.

The NI PXI-5401 uses a lookup waveform memory for storing the waveform and FIFO memory for storing the staging list, which contains multiple frequency list information. This FIFO is referred to as an instruction FIFO.

In Direct Digital Synthesis mode, each stage is made up of two instructions: the frequency and the time. The frequency instruction specifies the frequency of the waveform generation. The time instruction specifies the amount of time that the frequency generates.

Note  You cannot specify the number of iterations for a waveform to generate in Direct Digital Synthesis mode.