LeCroy PXA125, User Manual

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User Manual PXA125
Programming Reference 4-20
working memory.
The generator has nine built-in standard waveforms shapes. There is no need to download
waveform coordinates to the generator for it to be able to output one of these waveforms.
However, every time you select one of the standard functions, the firmware computes the
data and places the waveform coordinates in the working memory.
Not so if you want to generates arbitrary waveforms. In this case, you have to generate the
coordinates from an external application and then download the data to the generator. There
are two separate memory banks built into the instrument. The main and the largest memory
bank generates the arbitrary (USER) waveforms. This memory has vertical resolution of 14
bits and depth (or length) of 2 Meg. The other memory bank is used for arbitrary waveforms
that modulate the carrier frequency. This bank is completely different than the main memory
bank in the way that it contains data. Data structure for both memory types is given
hereinafter.
The SendBlock() function is used for sending arbitrary blocks of data to the instrument. Here
are some simple steps for you to follow in your application. Two examples are given: Using
the SendBlock() function with resident data array and using SendCommand() with an exter-
nal data file.
Example 1
1. Use SendCommand to program Trac:sel 1
2. Use SendCommand to program Trac:def 1,1000
3. Prepare your waveform data
4. Call SendBlock(hInstr, 1, "", (void*)wav, 1000*2). Note that each data point requires
2 bytes.
Example 2
1. Use SendCommand to program Trac:sel 1
2. Use SendCommand to program Trac:def 1,1000
3. Prepare your waveform data and save in a file. Concatenate the file name with
trace#
4. Call SendCommand(0,trac#<file_name>)
Arbitrary Waveform Data Structure
The arbitrary waveform data structure is actually very simple. It contains 16-bit words in the
range of –8192 to 8291, converted to short format (Intel binary representation)
Arbitrary FM Waveform Data Structure
The arbitrary FM waveform data structure is a bit more complicated. It is made of sample
clock frequencies and not as coordinates as was the structure for the arbitrary waveform
data. Sample clock range is from 50 S/s to over 100 MS/s. The arbitrary FM waveform mem-
ory has 200K points maximum however, you can choose to use shorter waveform length by
specifying the “size” parameter in the SendBlock() function.
Here are some simple steps that show how to prepare the arbitrary FM waveform data.
1. Define a structure:
Struct Fmtag( int pt;
char last;
}FMPT;