Chapter 1
Introduction to SCXI
©
National Instruments Corporation
1-17
Overview of SCXI Operation
This section describes on the SCXI analog input modules, and analog and
digital output modules used with DAQ devices.
Analog Input Modules
Table 1-1 lists the analog input modules. Analog SCXI modules can
operate in parallel or multiplexed mode. In parallel mode, the modules
perform no signal multiplexing and simply pass the conditioned signals
directly to corresponding channels on the DAQ device. Therefore, each
module is directly connected to its own DAQ device.
You will probably operate your analog SCXI modules in multiplexed mode.
You can multiplex thousands of conditioned analog input signals into a
single DAQ device. In this mode, connect the plug-in DAQ device to only
one SCXI module in a chassis. Digital lines on the DAQ device control the
modules and chassis. The DAQ device uses three or four digital output lines
and the EXTSTROBE line to program the SCXI system. In addition, a
digital input line is used for reading information back from the SCXI
modules.
When using SCXI analog input modules, you can measure analog input
signals by doing single-channel readings or hardware-timed,
multiple-channel scanning.
During single-channel readings, the DAQ device serially writes a digital
pattern to SCXI Slot 0, located in the chassis, indicating which SCXI
module to address. The DAQ device then writes a digital pattern to the
module indicating which input channel is to be read. This configures the
module to route the desired signal to the analog bus of the SCXI chassis.
Ultimately, the signal is routed to analog input channel 0 of the DAQ
device. The DAQ device then reads channel 0, as shown in Figure 1-7.
NI-DAQ automatically performs this low-level digital communication and
signal routing when you call the single-channel analog input functions.
