Chapter 2
Using the SCXI-1581
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National Instruments Corporation
2-5
SCXI-1581 User Manual
Theory of Multiplexed Hardware Operation
When you configure a module for multiplexed operation, the routing of
analog-input signals to the E Series DAQ device depends on the module in
the SCXI system to which the E Series DAQ device is cabled. There are
several possible scenarios for routing signals from the multiplexed modules
to the E Series DAQ device.
If the module you are scanning is not directly cabled to the E Series DAQ
device, the module sends its signals through the SCXIbus to the cabled
module. The cabled module, whose routing is controlled by the SCXI
chassis, routes the SCXIbus signals to the E Series DAQ device through the
CH0 pins on its rear signal connector shown in Figure 2-1. Because the
SCXI-1581 does not have any input channels to scan, multiplexed scanning
is the only scanning mode that is possible when the SCXI-1581 is the
cabled module.
If the module you are scanning is directly cabled to the E Series DAQ
device, the module routes its input signals through the CH0 pins on its rear
signal connector.
The power of SCXI multiplexed scanning is its ability to route many input
channels to a single channel on the E Series DAQ device. The number of
channels you can scan in multiplexed mode is limited to 512 channels per
chassis.
Immediately prior to a multiplexed scanning operation, the SCXI chassis is
programmed with a module scan list that controls which module sends its
output to the SCXIbus during a scan. Depending on which module you are
scanning, you can give the list of channels in a random order or you are
required to give the list in sequential order.
Refer to the appropriate user manual for information regarding the
procedure for scanning specific SCXI analog-input modules.