NOVATECH INSTRUMENTS 15 409C Manual Rev 1.12
allow upwards of 10 microseconds for this data to move,
the timing of the trigger update is decoupled from this
time uncertainty. Thus, this method enables the user to
more easily synchronize updates with external events.
External triggering can be used with the table and it can
also be used without the table when the user is sending
serial commands.
10.0 OPTION /E
SMA EXTERNAL CLOCK
10.1 Description. The 409C has a rear mounted BNC
connector labeled REF IN that accepts an external clock
of up to 500MHz. However, when option /R is installed
in the 409C, the functionality of the REF IN BNC is
changed. With option /R the REF IN BNC only accepts
a 10MHz external reference input and this 10MHz signal
is now routed to a daughter board inside the 409C. The
purpose of option /E is to restore the functionality of the
external clock. This is accomplished by adding an SMA
connector labeled EXT CLK to the 409C rear panel .
10.2 EXT CLK SMA. The EXT CLK SMA connector
accepts external signals up to 500MHz and functons
identically to that of the REF IN BNC on a 409C that
does not have option /R installed. Like a 409C without
option /R, the 409C/R/E and the 409C-AC/R/E both can
be programmed to use the signal on the EXT CLK SMA
input as the master clock. This is done by sending a C E
command.
10.3 Master Clock Selection. With both options /R
and /E installed the user has the following master clock
selection choices:
1) Use the internal oscillator by accepting the default C
x command of “C I’ and not connecting an external
10MHz signal.
2) Use the internal oscillator but have it disciplined by
an external 10MHz signal connected to the REF IN
BNC connector and accepting the default C x com-
mand of “C I”.
3) Use an external signal of up to 500MHz connected to
the option /E SMA connector labeled EXT CLK and
send a new C x command of “C E”
9.0 OPTION – AC
EXTERNAL TIMING CONTROL
9.1 Description. Option –AC adds two rear mounted
SMA connectors, labeled IOUD and TS, that can be used
for triggering and synchronizing 409C outputs. These
signals are in parallel with the IOUD and TS pins on the
rear mounted header connector J8. The logic levels for
these pins are 0V for logic 0 and 3.3V for logic 1.
9.2 IOUD Output vs Input. By default, the IOUD sig-
nal is an output indicating that the microcontroller has
triggered an update. The “I e” command changes IOUD
from an output to an input and requires that an external
trigger pulse IOUD high to update the 409C outputs.
9.3 IOUD Used as Output. The IOUD signal is pulled
down internally to ground. When the 409C microcon-
troller updates the 409C, it pulses IOUD high. The actu-
al trigger happens on the rising edge of this signal and
this rising edge can be read by the users hardware.
9.4 TS Input. The TS input connector is disabled by
default. It can be enabled using the IS command. When
enabled it functions just like the “TS” serial command.
If a table is not running and the TS input is enabled, then
applying a trigger signal to the TS connector will step
through the active rows of the table. The TS input is
pulled down inside the 409C. Pulsing the TS input high,
will trigger the update on the positive edge of the pulse.
An edge occurring sooner than the minimum dwell time
will be ignored.
9.5 External Triggering when IOUD is an Input.
The AD9959 DDS ASIC must be preloaded with a new
set of values prior to applying an external IOUD trigger.
Preloading is done with the TS command or by applying
a trigger signal to the TS connector. Once preloaded, the
409C can be triggered to update all outputs by applying a
trigger pulse to the IOUD connector. The trigger signal
must pulse IOUD high, the update will happen on the
rising edge.
9.6 More Precise Timing with External Triggering.
Using external triggering enables the user to take control
of exactly when the outputs are updated. This avoids the
uncertainty regarding the exact amount of time the pro-
cessor will take to move data from Table Flash to the
AD9959 DDS ASIC registers. While the user must still
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