7
DDS9m Manual
3.11 High Speed Interface Installation. The
DDS9m can also be controlled by using connections
to the 24-pin (12x2) header. See Table 4 for connec-
tor pinout and pin descriptions. Use of this port
requires detailed knowledge of the AD9959 DDS
generator IC. You can use the ‘B’ command to test
your operation.
NOTE:
The table mode or table RAM is not accessible from
the high speed port. The high speed port controls
only the DDS ASIC.
NOTE:
For maximum interface speed, the high-speed inputs
do not have additional protection against ESD
damage beyond that provided by the CMOS inputs
(+/-2kV, Human Body Model. +/-200 V, machine
model) and
47Ω
series resistors.
3.12 All of the inputs are 3.3V VHCMOS compati-
ble and require:
V
il
<= 0.4 volts
V
ih
>= 2.7 volts
3.13 C
in
on each pin is approximately 10pF (appli-
cation cable capacitance not included). The input
pins are series terminated with a 47
Ω
resistor. It is
recommended that a series termination resistor of
50-100
Ω
be used at each signal line source to pre-
vent reflections and ringing. The exact value will be
determined by your application circuitry and
cabling.
3.14 SER-, pin 4 of P1 must be held low to select
the high-speed interface. During initialization, EN-,
pin 11 of P1, is held high. When initialization is
complete it returns low.
3.15 Signal Outputs. There are eight signal outputs
on the DDS9m: four channels of Sine and the corre-
sponding LVCMOS/TTL. The Sine outputs are pro-
vided on MCX connectors (Johnson Components,
133-3701-133 or equivalent
)
on the board edge.
Simply connect your 50
Ω
application cable to
appropriate output. The LVCMOS outputs are on
wirepoints near the MCX outputs. The square pad is
the LVCMOS output and the round pad is ground. If
NOVATECH INSTRUMENTS
you are not using the LVCMOS/TTL output, it is
suggested that it be disabled by sending the
“A D”
(default is disabled) command for best system noise
performance.
3.16 Mounting. Five mounting holes are provided
on the board. These holes are electrically connected
to circuit common and may be used for shield con-
nections. Clearance is provided for up to 3mm diam-
eter screws. Please allow at least 3 mm clearance on
the bottom side when mounting to a conductive
chassis or case. Refer to Table 3 and Figure 1 for
locations.
NOTE:
The DDS9m is cooled by convection. Verify that
there is adequate free air flow around the board
when mounting in an enclosure. Approximately 2
Watts are dissipated.
4.0
Operation
4.1 Power on reset. After power is applied, the
DDS9m takes approximately 500ms to initialize.
Commands sent during this time will be ignored or
may cause erroneous operation.
4.2 Specifications are met within 15 minutes of
power-up in stable environment.
4.3 After the DDS9m has been installed in the cus-
tomer application system, all that is required for
operation is to send the appropriate serial commands
per Table 2.
4.4 The user host computer software must properly
format the serial commands. Incorrect formatting
will result in an error code being returned. See Table
1 for a list of error codes.
4.5 For maximum interface speed, it is suggested
that Echoing be disabled by the
“E d”
command.
This will allow the host to send characters at a faster
rate. Note that no flow control is provided. Depend-
ing upon your host, the DDS9m may not be able to
keep up with serial characters. The DDS9m will
respond with an
“OK”
for a correctly received data
command. You will have to verify correct operation
at your host rate.
