Stanford Research Systems DS345, Manual

Page: 57 / 139

Programming Commands
3-7
The following commands allow downloading arbitrary waveform and modulation patterns. The commands
have several things in common: First, the data are sent as multi-byte
binary
(not ASCII) data and the binary
data is followed by a checksum to ensure data integrity. The data is sent least significant byte
first
. The
checksum is just the sum of the data values sent, ignoring carries. Second, the commands are
queries-
that
is, after the command is received and processed the DS345 will return the ascii value 1 indicating that it is
ready to receive the binary data stream. When using these commands the program should wait for return val-
ue before sending the binary data. During the downloading of the binary data there is a 10 second receive
data timeout. That is, if more than 10 seconds elapses between successive data values an error will be gen-
erated and downloading aborted.
AMOD? i
The AMOD? query allows downloading arbitrary modulation patterns. The
modulation type must be set to AM, FM, or PM. i is the number of points to
be downloaded and is limited to 10000 AM points, 1500 FM points, and 4000
PM points. To generate an arbitrary modulation follow the following steps:
1) Send the query AMOD? i where i is the number of points in the waveform.
2) Wait until the DS345 returns "1" indicating that it is ready to receive data.
3) Send the modulation data (discussed below). The i data points are sent
least significant byte first. There should be i data points sent.
4) Send the checksum (the sum of i data points) least significant byte first.
Arbitrary AM:
Each arbitrary AM point is a 16bit integer value. This value is the fraction of
front panel amplitude to be output. The values range from 32767 = 1.0 * full
amplitude to -32767 = -1.0 * amplitude. The value for a desired modulation
fraction is easily calculated from the formula: value = 32767 * fraction. For
normal AM the values should range from 0 to 32767 (1.0), while for DSBSC
the -32767 (-1.0) to 32767 (1.0) range is used. The i data values should be
followed by a 16-bit checksum- simply the 16-bit sum of the data values.
Thus, a total of i+1 16-bit values will be sent. When modulation is enabled
each modulation point takes N*0.3
µ
s to execute, where N is the arbitrary
modulation rate divider (see the AMRT command). The MODULATION
OUTPUT will output the modulation waveform when modulation is enabled,
+5.0 V corresponds to 100% output and -5.0V corresponds to -100% modu-
lation.
Arbitrary FM:
Each arbitrary FM point is a 32 bit integer value. This value is the frequency
to be output. If the frequency is not allowed for the currently selected wave-
form an error will be generated. The 32 bit value is calculated from the for-
mula: value = 2 32 *(frequency/40 MHz). Thus, the j data points form a list of j
frequencies to be output. The i data values should be followed by a 32-bit
checksum- simply the 32-bit sum of the data values. Thus, a total of i +1 32-
bit values will be sent. When modulation is enabled each modulation point
takes N*2.0
µ
s to execute, where N is the arbitrary modulation rate divider
(see the AMRT command). The MODULATION OUTPUT will output the
modulation waveform when modulation is enabled, with 0 V corresponding to
the minimum frequency and 5.0 V corresponding to the maximum frequency
in the modulation pattern.