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Chapter 3
Theory of Operation
Analog Output Circuitry
Output Stage and
Hardware Scan Control
Reference
SCXI-1121 User Manual
Figure 3-6 shows the SCXI-1121 analog output circuitry.
Channel 0
Channel 1
Output
Mux
Channel 2
Channel 3
MTEMP
Analog
The SCXI-1121 output circuitry consists of a buffered-output multiplexer
and channel-select hardware. The channel-select hardware consists of a
two-bit counter, MUXCOUNTER. This counter is needed when the board
is operating in the Multiplexed-Output Mode. The counter output is sent to
the multiplexer address pins to determine which of the four channels is to
be connected to MCH0. In the Single-Channel Read mode, the
MUXCOUNTER is loaded with the desired channel number. In the
Scanning mode, the counter is loaded with the first channel to be read.
During the scan, the counter is clocked by SCANCLK from the data
acquisition board, or TRIG0 from the SCXIbus, depending on the state of
the CLKSELECT bit in the Configuration Register. During scanning
operations, the MUXCOUNTER is reloaded with the channel value stored
SCXIbus
AB0
Switch
Buffer
MCH1+
From
Channel 1
MCH2+
From
Channel 2
From
MCH3+
Channel 3
DTEMP
Figure 3-6. Analog Output Circuitry
3-12
Output
Stage
Control
MCH0+
MCH0–
MCH1–
MCH2–
MCH3–
MCH4+
MCH4–
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