NI SCXI-1127 User Manual page 46

Chapter 2 Using the SCXI-1127
Front Connector
Backplane
Connector
From
DMM AUX
SCXI-1127 User Manual
Hardware Timed Scanning Using an NI-DMM
When using an NI-DMM with the SCXI-1127, synchronous mode is the
only mode in which the NI-DMM and the SCXI-1127 operate. The
NI-DMM issues a trigger to advance the multiplexer at regular intervals.
The NI-DMM and the software guarantee that the switch has fully settled
before the next measurement is taken.
The module that connects directly to the digital connector on the
HVAB-backplane adapter is referred to as the cabled module. If you add
additional SCXI-1127 modules to your system the trigger is bused over the
SCXI backplane (Trig 0) allowing other modules to be triggered, as shown
in Figure 2-12. These additional modules are referred to as non-cabled
modules because they do not require the DMM to be cabled directly to
them.
Front Connector
RSC SCXI-Module
HVAB
Connector
Figure 2-12. Cabling an NI-DMM and Using the TRIG0 to Bus the VMC/EXT_TRIG_IN
Hardware Timed Scanning Using External Instruments
When using the SCXI-1127 with an external measurement instrument, you
can use either synchronous or handshaking mode to advance the
SCXI-1127.
Synchronous Scanning
In the synchronous scanning mode, the measuring device such as a DMM
issues a trigger, voltmeter complete (VMC), to advance the multiplexer at
regular intervals. Each interval must be at least 10 ms to guarantee that the
switch has fully settled before the next measurement is taken. For example,
you can connect the VMC of your DMM to the SCXI-1127 via a screw
Front Connector
SCXI-Module
to Non-Cabled Modules
2-14
Trig 0 (Backplane)
© National Instruments Corporation