HP E1419A User Manual page 172

The vertical slider controls the value of "offset" and the horizontal slider
controls the variable "inc". When the toggle switch is in the DDS(direct
digital synthesis) mode, the horizontal slider modifies "inc" to generate
lower resolution/higher frequency waveforms. When in the PPC(point per
cycle) mode, the slider modifies the ALG:SCAN:RATIO command of
Algorithm 1 to vary how many trigger cycles to wait before executing the
algorithm and writing different data to the output channel . This has the
effect of slowing down the waveform and lowering its frequency. Algorithm
2 simply copies each value of channel 132 to the FIFO every trigger cycle.
With Algorithm 1 only executing at some multiple of the trigger rate, there
will be repeated FIFO readings of the same value indicating a slower
frequency.
The "Offset/Frequency" object has the SCPI commands used to control the
scalar variable updates, and the object "Download Waveform" controls
writing to the array "waveform" in Algorithm 1.
Chapter 5 HP VEE Programming Examples 171