National Instruments SCXI-1121 Manuel D’Utilisation
Chapter 3
Theory of Operation
3-18
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entry. The list in Slot 0 will determine which module is being accessed and
for how many samples. It is important that you make sure that the lists on
the data acquisition board and Slot 0 are compatible so that the samples are
acquired as intended. See your SCXI chassis manual for more information.
for how many samples. It is important that you make sure that the lists on
the data acquisition board and Slot 0 are compatible so that the samples are
acquired as intended. See your SCXI chassis manual for more information.
Single-Module Multiplexed Scanning
Single-Module Multiplexed Scanning (Direct)
This is the simplest multiplexed scanning mode. Directly cable the
SCXI-1121 to the data acquisition board as shown in Figure 3-8. The
module sends SCANCLK onto TRIG0, and Slot 0 sends SCANCON back
to the module. SCANCON will be low at all times during the scan except
during changes from one Slot 0 scan list entry to the next, when
SCANCON pulses high to make the MUXCOUNTER reload its starting
channel. Notice that although you are using only a single module, you can
put many entries with different counts in the Slot 0 FIFO, so that some
channels are read more often than others. You cannot change the start
channel in the module Configuration Register during a scan.
SCXI-1121 to the data acquisition board as shown in Figure 3-8. The
module sends SCANCLK onto TRIG0, and Slot 0 sends SCANCON back
to the module. SCANCON will be low at all times during the scan except
during changes from one Slot 0 scan list entry to the next, when
SCANCON pulses high to make the MUXCOUNTER reload its starting
channel. Notice that although you are using only a single module, you can
put many entries with different counts in the Slot 0 FIFO, so that some
channels are read more often than others. You cannot change the start
channel in the module Configuration Register during a scan.
Figure 3-8. Single-Module Multiplexed Scanning (Direct)
Single-Module Multiplexed Scanning (Indirect)
In this mode, the SCXI-1121 is not directly cabled to the data acquisition
board. Instead, you connect another module to the data acquisition board,
and the analog output of the SCXI-1121 is sent over Analog Bus 0, through
the intermediate module, and then to the data acquisition board. The
SCXI-1121 receives its MUXCOUNTER clock from TRIG0, which is sent
by the intermediate module, as illustrated in Figure 3-9. Slot 0 operation is
the same for direct connection scanning.
board. Instead, you connect another module to the data acquisition board,
and the analog output of the SCXI-1121 is sent over Analog Bus 0, through
the intermediate module, and then to the data acquisition board. The
SCXI-1121 receives its MUXCOUNTER clock from TRIG0, which is sent
by the intermediate module, as illustrated in Figure 3-9. Slot 0 operation is
the same for direct connection scanning.
Cable
Assembly
Data Acquisition Board
Analog Input
Timing Output
TRIG0
SCANCON X
SCANCLK
MCH0
SLOT 0
Four Isolated
Floating
Single-Ended
Inputs
SCXI-1000 or SCXI-1001 Chassis
SLOT X
SCXI-1121