Multiple-module multiplexed scanning, Multiple-chassis scanning – National Instruments SCXI-1121 User Manual
Page 103
Chapter 5
Programming
5-12
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2.
Program the other module not to drive Analog Bus 0, but to send
Analog Bus 0 to the data acquisition board. Also program the other
module to send a SCANCLK*-compatible signal to TRIG0.
3.
Write the binary pattern
01S
c
XXXCC XX001111
to the SCXI-1121
Configuration Register, where CC is the starting channel number.
Multiple-Module Multiplexed Scanning
To scan multiple modules, you must connect one module to the data
acquisition board and the module must be able to transfer Analog Bus 0 to
the data acquisition board. This module must also be able to send a
SCANCLK*-compatible signal on TRIG0. See Chapter 2,
, for more information. The module programming steps are
as follows:
1.
Perform any necessary programming to ensure that no modules are
driving Analog Bus 0. For an SCXI-1121, clearing AB0EN in the
Configuration Register will ensure that its output is not driving AB0.
2.
Program the module that is connected to the data acquisition board to
connect Analog Bus 0 to the data acquisition board but not drive
Analog Bus 0 unless it is receiving an active low signal on SCANCON.
Also program the module to send a SCANCLK*-compatible signal
onto TRIG0. If this module is an SCXI-1121, this programming is
accomplished by writing the binary pattern
10S
c
XXXCC XX001111
to
its Configuration Register.
Note
If this module is an SCXI-1121 and is not going to be scanned (it is just being used
as an interface), write a zero to bit 2 (SCANCONEN) in the Configuration Register. The
start channel bits become don't care bits.
3.
Program the other modules to be used in the scan to connect their
outputs to Analog Bus 0 but not to drive Analog Bus 0 unless receiving
an active low signal on SCANCON. Also program the other modules
to use TRIG0 as their clock source. For SCXI-1121 modules, this
programming is accomplished by writing the binary pattern
01S
c
XXXCC XX001111
to their Configuration Registers.
Multiple-Chassis Scanning
To scan modules on multiple chassis, you must use the SCXI-1001. The
cable from the data acquisition board must bus the digital lines to one
module on each chassis. Additionally, the cable must provide each chassis
with its own analog channel. The data acquisition board must be able to
take several readings at a time on a given channel before accessing a new