Programming instructions

Chapter 5 Things You Should Know about Analog Input
LabVIEW Data Acquisition Basics Manual 5-14
© National Instruments Corporation
The AMUX-64T Scanning Order
This section explains how LabVIEW scans channels from the AMUX-64T.
You must know this scanning order so that you can determine which analog
input channel LabVIEW scanned during a data acquisition operation.
The scanning counters on the AMUX-64T and on the DAQ device
perform automatic scanning of the AMUX-64T analog input channels.
When you perform a multiple-channel scanned data acquisition with an
AMUX-64T, a counter on the DAQ device switches the DAQ device
multiplexers.
When you connect a single AMUX-64T device to the DAQ device, you
must scan four AMUX-64T input channels for every DAQ device channel.
If you attach two AMUX-64T devices to the DAQ device, LabVIEW
scans eight AMUX-64T channels for every DAQ device input channel.
For example, assume that channels 0 through 3 on AMUX-64T device 1
and channels 0 through 3 on AMUX-64T device 2 are multiplexed together
into DAQ device channel 0. In this case, LabVIEW scans the first four
channels on AMUX-64T device 1, followed by the first four channels on
AMUX-64T device 2.
If you attach four AMUX-64T devices to the DAQ device, LabVIEW
scans 16 AMUX-64T channels for every DAQ device input channel.
For example, channels 0 through 3 on AMUX-64T device 1, 2, 3, and 4 are
multiplexed together into DAQ device channel 0. In this case, LabVIEW
scans the first four channels on device 1, followed by the first four channels
on device 2, the first four channels on device 3, and then the first four
channels on device 4.
The order in which LabVIEW scans channels depends on the channel list
you specify in the AI Group Config VI. You specify this channel list as
an array of DAQ device channel numbers indicating the order in which
LabVIEW scans the DAQ device channels. When scanning multiple
channels, list only the device channels—not the AMUX-64T channels.
(You only use the
AMy!x
syntax in your channel list when you sample
a single AMUX-64T channel.) LabVIEW then scans four, eight, or
16 channels for every device channel for one, two, or four AMUX-64T
devices, respectively. However, the AMUX-64T has a fixed scanning order.