Teledyne LeCroy PXA125 - Manual (Page 26)

User Manual PXA125
1-12 Portrayal
Standard (FIXED)
Waveforms
The PXA125 must pre-load its memory before it can generate
waveforms. On power up, the waveform memory has no specific
data. The sine waveform, being the default waveform on power on, is
computed and loaded to the waveform memory as part of the reset
procedure. From this moment on, every time that another standard
waveform is selected, it is being computed and loaded to the
waveform memory.
Waveforms are written from the same start address. Therefore, every
time that a new waveform is selected, there is some minimal time for
the processor to compute and download the data to the memory.
The PXA125 can be programmed to output one of nine standard
waveform shapes: sine, triangle, square, pulse/ramp, sine(x)/x pulse,
gaussian pulse, rising/decaying exponential pulse, noise and dc.
There are some parameters associated with each waveform, which
modify the shape of the waveform to better suit your needs. For
example, different start phase for the sine waveform can be
programmed for each channel to create phase offsets between the
two instruments.
Arbitrary (User)
Waveforms The arbitrary waveform memory is capable of storing one or more
user-defined waveforms. As was discussed before, the PXA125 is
supplied with 2 Meg memory bank. There are up to 2 Meg points that
can be allocated to one single waveform. On the other hand, there is
no need to use the entire memory for only one waveform; The
memory can be divided into smaller segments and loaded with
different waveforms and the instrument can be programmed to output
one segment at a time.
Loading data to arbitrary waveform memory can be a time-consuming
task, especially if all 2 Meg points are loaded in one shot. The
PXA125 utilizes a DMA (direct memory access) concept that speeds
data transfer from host computer to the instrument.