User Manual LW120
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. DMA download is terminated with the MSBit of the last byte set to 1.
As an example, lets compute the number that has to be downloaded for a sample clock value of
15.23456MHz. Using the equation N = SCLK [Hz] x 14.31655765, we compute
N = 15.23456MHz x 14.31655765 = 218106456.5, rounded to 218106457 = 0x0D000A58
0
0 0 0 0 n
m
0 0 0 0
0 1
1
1
0 0 0 0 0 0 0 0
0 0 0 0
0
0
1
1
1
1 1 0 0 0
0
0
D7
D0
MSB
LSB
0D
00
0A
58
m = 0 standard byte
m = 1 DMA off
n = 0 no marker
n = 1 marker on
0
Figure 4-8
. FM Modulating Waveform Data Strructure
The bytes are downloaded to the DMA port byte at a time. The first byte is the MSByte and the last is the
LSByte. The LSByte is a control byte and is interpreted as follows:
0x00 – normal data byte, no marker bit
0x01 – normal data byte, marker bit on
0x80 – DMA termination byte, no marker bit
0x81 – DMA termination byte, marker bit on
DMA:TYPE?
Response and default
The LW120 will return WAVE, or FM depending on present setting. Default value is WAVE.
Remote Programming Reference 4-57