3
DDS9m Manual
extensive filtering is used on the DDS9m board, a
quiet and well regulated power supply will ensure
optimum performance. If switching power supplies
are used, please verify that your system noise
requirement is met.
3.3 RS232 Installation. To use the DDS9m in the
RS232 mode, connect your host computer to the 9-
pin female RS232 connector on the DDS9m. If you
are using a PC, a 9-pin monitor extension cable used
as an RS232 cable will allow direct connection to
the DDS9m without the use of a null modem cable
or gender changer. If you are using a different com-
puter, terminal or other control source, please note
that the data TO the DDS9m is on pin 3; the data
FROM the DDS9m is on pin 2 and the COMMON
return is on pin 5. Set your host to 19.2 kbaud, 8 bits,
1 stop bit, no parity and no hardware flow control.
See Table 2 for RS232 Serial Commands.
3.4 You may use a USB to RS232 adapter cable
with computers that do not provide a serial port. Fol-
low the manufacturer’s installation instructions
when using a USB adapter.
3.5 Commands are not case sensitive. There must
be a space after each command except
R
,
CLR
,
S
and
QUE
. End with any combination of
CR
,
LF
or
CRLF.
Illegal commands will result in an error
code being returned per Table 1.
3.6 The
“QUE”
command returns five hexadecimal
strings reflecting the present state of the DDS9m.
NOVATECH INSTRUMENTS
See page 9 for an explanation of the values that
make up these strings. Note that the frequency set-
tings will be scaled as discussed below if an external
clock is used.
3.7 The
“B”
command can cause erroneous opera-
tion and must be used with care. Detailed knowledge
of the operation of the Analog Devices AD9959
DDS generator is required. Since all registers are
accessible, it is possible to set the board into a non-
functional mode, requiring a reset. Application Note
AN001 shows an example of the command for set-
ting frequency.
NOTE:
The program SOF8 is available for the DDS9m.
This program provides a graphical interface for all
the serial commands, allowing simple control of the
DDS9m. The SOF8 CD contains multiple versions
of the software. Be sure to read the README file to
see which is appropriate for your instrument.
3.8 Internal Clock. If you plan to use the DDS9m
internal clock, which is the default setup mode, no
action is required. If the DDS9m was previously set
to use the external clock, send the serial command
“C i”
to reselect the internal clock. If you wish to
maintain this setting, use the save command
“S”
.
3.9 External Clock. If you are providing your own
clock source, send the serial command
“C e”
.
Apply your clock to the External Clock Input MCX
on the board. Note that phase noise and stability are
dependent upon your supplied clock. See specifica-
tions for signal levels required and acceptable fre-
quency range. If you wish to maintain this setting,
use the save command
“S”
.
3.10 The external clock can also be used with Kp=1
for direct connection to the DDS generator. With
Kp=1, the PLL multiplier is disabled. Use this direct
input, up to 500MHz, for optimum phase noise per-
formance.
NOTE:
When using an external clock, frequency scaling of
the
“Fn”
command may be required. Please see
Operation, Section 4, for details.
Table 1: RS232 Error Codes
Error Code
Meaning
OK
Good command received (not sent for
R, CLR and QUE)
?0
Unrecognized Command
?1
Bad Frequency
?2
Bad AM Command
?3
Input line too long
?4
Bad Phase
?5
Bad Time
?6
Bad Mode
?7
Bad Amp
?8
Bad Constant
?f
Bad Byte
