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2.
Convert the result from 1 above to 4-byte (32-bit) binary word and union with an 8-bit control word as
shown in Figure 4-8 (Refer to Downloading FM Modulating Waveforms Using DMA).
3.
Use an I/O routine such as ViMoveAsync (from the VISA I/O library) to transfer binary blocks of data to
the generator.
4.
Last data point is sent with MSB bit set to "1"; Data transfer is completed and CPU resumes control.
There are a number of points you should be aware of before you start preparing the data:
6. The FM function is shared by both channels
7. The number of bytes in a complete FM modulating waveform data must divide by 5. The Model LW120
has no control over data sent to its FM waveform during data transfer. Therefore, wrong data and/or
incorrect number of bytes will cause errors
8. The LSBit on the last byte sets marker position. "0" = sets no marker and "1" sets marker. You can set
as many markers as you want.
9. The SYNC output serves as marker output when you have the LW120 set to operate in FM mode.
Normal SYNC level is TTL low. The SYNC output is set to TTL high when the marker bit is true. This
way you can use the SYNC output to mark frequency occurrences during FM operation.
10. Data download is terminated with the MSBit of the last byte set to 1.
FM:DEViation<deviation>
Purpose
This command will set the deviation frequency in units of samples per second.
•
<deviation> sets the phase offset between the channels. Phase offset is in waveform points
Parameter type
Numeric
Parameter range
<deviation>
1e-3 to 100e6 in units of samples per second
FM:DEViation?
Response and default
The LW120 will return the present frequency deviation value. The returned value will be in standard
scientific format (for example: 100mHz would be returned as 100E-3 – positive numbers are unsigned).
Default value is 1e3. Default value is 1e6.
FM:FUNCtion:MODE(FIXed|USER}
Purpose
This command will set the frequency modulating waveform mode to FIXed (standard) and USER (arbitrary)
waveforms.
•
FIXed will enable a library of built in standard waveforms
•
USER will set the generator to accept arbitrary waveform from an external application
Parameter type
Discrete
FM:FUNCtion:MODE?
Response and default
The LW120 will return FIX, or USER depending on its present setting. Default is FIX.
Remote Programming Reference 4-20
User Manual LW120
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