Publication No. 980935 Rev. A
3152B User Manual
EADS North America Test and Services
Programming Reference 5-103
Synchronization
Commands
The synchronization commands control synchronization aspects to an
external source via the PLL input; These also control synchronization
via the backplane ECLTrg0 line to an adjacent module. Although
synchronization through the ECLTrg0 line is limited in their upper
frequency range (60 MHz maximum), this set of synchronization
commands was kept for backward compatibility with the legacy
3152A. Contrary to the legacy synchronization commands, modern
synchronization scheme is achieved using the instrument control
commands where local bus (LBUS0-7) lines are utilized to share high
frequency signals between channels and adjacent slots.
As was mentioned above, there are two methods of synchronizing
multiple 3152Bs inside one VXIbus chassis. The first is through the
ECLT0 and ECLT1 lines that provide the necessary signal to achieve
lock between modules. Using this method, one instrument is
configured as master and the rest of the instruments are configured
as slaves. When synchronized, the slave instruments are initially
locked to the start phase on the master module but later can be
configured to have phase offsets relative to the master module. Phase
offset is programmable from 0
°
to 360
°
. 3152Bs modules can be
inserted in any slot, not necessarily adjacent, to be able to phase
synchronize between modules.
Another way to lock the 3152 to an external reference is its PLL input.
Using the PLL function, a reference signal is applied to the trigger
input; The signal is being detected automatically by the auto-detection
circuit that, in turn, sets up the lock-in range and prepares the PLL
circuits to a final lock. After lock, the frequency and the start phase of
the reference are duplicated by the 3152B. A front-panel LED
illuminates when the reference signal is valid and the instrument locks
on the external signal. Additional control allows phase shifting of the
locked instrument from -180
°
to +180
°
in reference to the input signal.
Hardware shift of the start phase is accomplished using the PM input,
where dc to 10 KHz voltage levels can phase modulate the locked
instrument.
The synchronization commands are summarized in Table 5-14.
Phase offset resolution depends on the number of waveform samples.
For instance, if you have 1000 waveform samples, there is no
problem with adjusting the phase offset in 1o increments (360o / 1000
< 1). As another example, if you have only 10 waveform samples, the
best phase offset increments are only 36o (360o / 10 = 36o). There is
a special fine adjustment for phase offset with a 36o range. This
adjustment is useful in places where a 36o gap is too wide. The fine
phase adjustment improves phase offset settings to 0.01o and can be
used in conjunction with the coarse phase offset adjustment at any
phase offset setting point.
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