National Instruments SCXI-1121 - Manual (Page 79)

Chapter 3 Theory of Operation
© National Instruments Corporation 3-17 SCXI-1121 User Manual
Scanning Modes
There are four basic types of scanning modes possible with the
SCXI-1121—single-module parallel scanning, single-module multiplexed
scanning, multiple-module multiplexed scanning, and multiple-chassis
scanning (possible only with the SCXI-1001 chassis). For additional
information, consult Chapter 2,
Configuration and Installation , Chapter 5,
Programming , your data acquisition board manual, and your SCXI chassis
user manual. If you need further information, contact National Instruments.
Single-Module Parallel Scanning
Single-Module parallel scanning is the simplest scanning mode. Directly
cable the SCXI-1121 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-1121.
Figure 3-7. Single-Module Parallel Scanning
Multiplexed Scanning
Only the MIO-16 data acquisition boards support multiplexed scanning on
the SCXI-1121. During multiplexed scanning, a module sends the
SCANCLK signal to Slot 0 over the TRIG0 backplane line, and Slot 0
sends unique SCANCON signals to each module. Each module uses its
signal to reload MUXCOUNTER and to determine when the SCXI-1121
output is enabled. Slot 0 contains a module 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
Four Isolated
Floating
Single-Ended
Inputs
CH0
CH1
CH2
CH3
MCH0
MCH1
MCH2
MCH3
Analog Input 0
Analog Input 1
Analog Input 2
Analog Input 3
Data Acquisition Board SCXI-1121
Cable Assembly