National Instruments SCXI-1120 - Manual (Page 81)

Programming Chapter 5
SCXI-1120 User Manual 5-10 © National Instruments Corporation
also be able to send a SCANCLK*-compatible signal on TRIG0. See Chapter 2, Configuration
and Installation, 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-1120, 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-1120, this programming is accomplished by writing
the binary pattern
10XXXCCC XX001111 to its Configuration Register.
Note: If this module is an SCXI-1120 and is not going to be scanned (it is just being used as
an interface), write a 0 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 drive Analog Bus 0 unless receiving an active low signal on SCANCON. Also
program the modules to use TRIG0 as their clock source. For SCXI-1120 modules, this
programming is accomplished by writing the binary pattern
01XXXCCC XX001111 to
their Configuration Registers.
Multiple-Chassis Scanning
To scan modules on multiple chassis, you must use the SCXI-1001 chassis. 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 channel. See
the Counter 1 and SCANDIV subsection of the 1. Data Acquisition Board Setup Programming
section earlier in this chapter. You can use the MIO-16 boards, in conjunction with the
SCXI-1350 multichassis adapter, for multichassis scanning.
For each chassis, program the modules according to the appropriate mode of operation,
disregarding the fact that other chassis will be involved.
For example, you want to scan thirteen modules. Twelve modules are in one chassis, and the
thirteenth is in the second chassis and is to be scanned through a fourteenth module that is cabled
to the data acquisition board but is not involved in the scan. Program the twelve modules in the
first chassis according to the steps in the previous Multiple-Module Multiplexed Scanning
section, and program the thirteenth and fourteenth modules according to Channel Scanning from
the SCXI-1120 via Another Module earlier in this chapter.
3. Programming the Slot 0 Hardscan Circuitry
The following section describes how to program the Slot 0 circuitry for scanning operations. For
a more detailed description of the Slot 0 scanning circuitry, consult the SCXI-1000/1001 User
Manual. Descriptions of the Slot 0 registers are in the Slot 0 Register Descriptions section of
Chapter 4, Register Descriptions. It is not necessary to read this section if you are performing
single-module parallel scanning.