Theory of Operation
Chapter 3
SCXI-1120 User Manual
3-14
© National Instruments Corporation
data acquisition board user manual, or your SCXI chassis user manual. If you need more
information, contact National Instruments.
Single-Module Parallel Scanning
Single-module parallel scanning is the simplest scanning mode. Directly cable the SCXI-1120 to
the data acquisition board as shown in Figure 3-7. In this configuration, each analog signal has
its own channel. Timing signals are not necessary for this type of scanning because the module
provides all channels to the data acquisition board at all times. You can implement
single-module parallel scanning with any data acquisition board that is appropriately cabled to
the SCXI-1120.
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
SCXI-1120
Data Acquisition Board
Cable Assembly
Eight Isolated
Floating
Single-Ended
Inputs
MCH0
MCH1
MCH2
MCH3
MCH4
MCH5
MCH6
MCH7
Analog Input 0
Analog Input 1
Analog Input 2
Analog Input 3
Analog Input 4
Analog Input 5
Analog Input 6
Analog Input 7
Figure 3-7. Single-Module Parallel Scanning
Multiplexed Scanning
Only the MIO-16 data acquisition boards support multiplexed scanning on the SCXI-1120.
During multiplexed scanning, a module sends the SCANCLK signal to Slot 0 over the TRIG0
backplane line, and Slot 0 sends SCANCON signals to each module. Each module uses its
SCANCON signal to reload MUXCOUNTER and to determine when the SCXI-1120 output is
enabled. Slot 0 contains a module scan list first-in-first-out (FIFO) memory chip, similar to the
Channel/Gain FIFO on an MIO-16 board, except that instead of having a channel number and
gain setting for each entry, the Slot 0 FIFO contains a slot number and a sample count for each
entry. The list in Slot 0 will determine which module is being accessed and for how many
samples. It is important that you make sure that the lists on the data acquisition board and Slot 0
are compatible so that the samples are acquired as intended. See your SCXI chassis manual for
more information.
Single-Module Multiplexed Scanning
Single-Module Multiplexed Scanning (Direct)
This is the simplest multiplexed-scanning mode. Directly cable the SCXI-1120 to the data
acquisition board as shown in Figure 3-8. The module sends SCANCLK onto TRIG0, and Slot 0
sends SCANCON back to the module. SCANCON will be low at all times during the scan
