User Manual LW120
The LW120 will return 1 if the FM is on, or 0 if the FM is off. Default is 0.
FM:DATA#<header><binary_block>
Purpose
This command will download FM modulating waveform data in binary download. Using this command,
Arbitrary FM waveform table data is loaded to the LW120 using high-speed binary transfer in a similar way
to downloading waveform data with the trace command. High-speed binary transfer allows any 8-bit bytes
(including extended ASCII code) to be transmitted in a message.
FM:DATA#3100<binary_block>
This command causes the transfer of 10 bytes of data to the arbitrary FM waveform memory. The <header>
is interpreted this way:
•
The ASCII "#" ($23) designates the start of the binary data block.
•
"3" designates the number of digits that follow.
•
"100" is the number of bytes to follow. This number must divide by 5.
The generator accepts binary data as 40-bit integers, which are sent in five-byte words. Therefore, the total
number of bytes is always five times the number of arbitrary FM waveform points. For example, 100 bytes
are required to download 20 arbitrary FM waveform points. The IEEE-STD-488.2 definition of Definite
Length Arbitrary Block Data format is demonstrated in Figure 4-1 (refer to the TRACe subsystem). The
transfer of definite length arbitrary block data must terminate with the EOI bit set. This way, carriage-return
(CR – 0dH) and line feed (LF – 0aH) characters can be used as sequence data and will not cause
unexpected termination of the arbitrary block data.
•
<binary_block>
Represents arbitrary FM waveform data.
Downloading data to the arbitrary FM waveform memory is very different than loading arbitrary waveform
data. Waveform data programs amplitude domain therefore, every point programs an amplitude level. On
the other hand, FM modulating waveform data programs frequency domain therefore, every point sets
different sample clock frequency. The FM modulating waveform data is made of 40-bit words. However, the
GPIB link has 8 data bas lines and accepts 8-bit words only. Therefore, the data has to be prepared as 40-
bit words and rearranged as five 8-bit words before it can be used by the LW120 as FM modulating
waveform data. Figure 4-8 shows how to prepare the 40-bit word for the FM modulating waveform.
There are a number of points you should be aware of before you start preparing the data:
1. The FM function is shared by both channels
2. 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
3. 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.
4. 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.
5. Data download is terminated with the MSBit of the last byte set to 1.
The following sequence should be used for downloading arbitrary FM Waveforms:
1.
Prepare your FM waveform data points using the following relationship:
N = SCLK [Hz] x 14.31655765
Remote Programming Reference 4-19
