National Instruments SCXI-1120 - Manual (Page 75)

Programming Chapter 5
SCXI-1120 User Manual 5-4 © National Instruments Corporation
Multiplexed Output
To perform a direct multiplexed output measurement, you must cable the SCXI-1120 rear signal
connector to a data acquisition board. See Chapter 2, Configuration and Installation, for more
information. For information on how to make the voltage measurement with your data
acquisition board, consult your data acquisition board user manual. Remember to account for the
gains of both the SCXI-1120 and the data acquisition board when calculating the actual voltage
present at the input of the SCXI-1120.
To measure one of the eight differential input channels to the SCXI-1120, perform the following
steps:
1. Write the binary pattern 00XXXXCC XX000000 to the SCXI-1120 Configuration Register.
2. Measure the voltage with the data acquisition board.
To measure the voltage on the MTEMP line, perform the following steps:
1. Write the binary pattern 00XXXXXX XX100000 to the SCXI-1120 Configuration Register.
2. Measure the voltage with the data acquisition board.
Indirect Measurements
Indirect measurements involve one module sending a signal to Analog Bus 0, where it is picked
up by another module and transmitted to the data acquisition board.
Measurements from Other Modules
To perform measurements from other modules, you must cable the SCXI-1120 rear signal
connector to a data acquisition board. See Chapter 2, Configuration and Installation, for more
information. To make a measurement from another module, perform the following steps:
1. Perform any necessary programming to ensure that no modules are driving Analog Bus 0.
For an SCXI-1120, clearing AB0EN in the Configuration Register will ensure that its output
is not driving AB0.
2. Write the binary pattern 00XXXXXX XX100011 to the SCXI-1120 Configuration Register.
This step disables the SCXI-1120 from driving Analog Bus 0 and allows Analog Bus 0 to
drive MCH0 through the output buffer.
3. Program the other module to drive Analog Bus 0 with the signal to be measured.
4. Measure the voltage with the data acquisition board.
Measurements from the SCXI-1120 via Another Module
To perform measurements via another module, you must cable the other module rear signal
connector to a data acquisition board. The other module must be able to transfer Analog Bus 0 to
the data acquisition board. See Chapter 2, Configuration and Installation, for more information.