National Instruments SCXI-1120 - Manual (Page 74)

Chapter 5 Programming
© National Instruments Corporation 5-3 SCXI-1120 User Manual
7. Pull SLOT0SEL* low to deassert the SS* line, latch the data into the Configuration Register
and establish conditions for writing a new slot-select number to the Slot 0 Slot-Select
Register.
8. If you are not selecting another slot, write zero to the Slot 0 Slot-Select Register. If you are
selecting another slot, start at step 3.
For a timing illustration of a Configuration Register write, see Figure 2-15, Configuration
Register Write Timing Diagram, which shows the proper write to configure an SCXI-1120 that is
directly cabled to an MIO-16 board for multiple-module multiplexed scanning with a start
channel of 3.
Initialization
The SCXI-1120 powers up with its Configuration register cleared to all zeros. You can force this
state by sending an active low signal on the RESET* pin of the SCXIbus connector. In the reset
state, CH0 through CH3 are routed to MCH0 through MCH3 on the rear signal connector. The
module is disconnected from Analog Bus 0 and disabled from scanning.
Single-Channel Measurements
This section describes how to program the SCXI-1120, either alone or in conjunction with other
modules, to make single-channel, or nonscanned, measurements.
Direct Measurements
Parallel Output
To perform a parallel output measurement, you must cable the SCXI-1120 rear signal connector
to a data acquisition board with each output connected to a different data acquisition board
channel. 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, or the DTEMP line if
the module has been configured appropriately, perform the following steps:
1. Write the binary pattern 00XXX000 XX000000 to the SCXI-1120 Configuration Register.
Notice that this can be the RESET state.
2. Measure the voltage with the data acquisition board.