Chapter 5
Theory of Operation
©
National Instruments Corporation
5-3
The Configuration Register configures the SCXI-1104/C module for the
desired scanning mode and connection to the rear signal connector. The
EEPROM Register is the address for interfacing with the module
EEPROM, which contains calibration information. The Channel Register
selects a channel for a single measurement or a start channel for a scan.
Analog Circuitry and Front Signal Connector
The analog circuitry per channel consists of a lowpass filter amplifier and
a divide-by-10 attenuator. The channels are multiplexed to a single output
buffer.
Analog Input Channels
Each of the 32 analog input channels feeds a separate amplifier and the
signal passes through a three-pole lowpass filter.
For measurement accuracy of 0.012% of full scale, the minimum scan
interval is 3
µ
s. This is the smallest interval in which you can switch
between analog channels on the module and still measure voltages
accurately. The 3
µ
s interval gives you a maximum sampling rate of
333 kHz. Because this rate is much higher than the bandwidth of a single
SCXI-1104/C channel, you can sample multiple channels on multiple
SCXI modules without undersampling one of the SCXI-1104/C channels.
Analog Bus Switches
The SCXI-1104/C module contains switches to route the multiplexer
output to the SCXIbus. The SCXI-1104/C module also contains a switch to
receive a signal placed on the SCXIbus by another SCXI module. The
output buffer of the cabled module drives a received signal onto the
MCH0+ line of its rear signal connector so that the DAQ device can read
it. When a signal passes on the SCXIbus from the scanned SCXI module to
the cabled SCXI module, the measurement is known as
.
