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© National Instruments Corporation
5-1
SCXI-1100 User Manual
Chapter 5
Programming
This chapter contains a functional programming description of the SCXI-1100 and Slot 0.
Note: If you plan to use a programming software package such as NI-DAQ, LabWindows, or
LabVIEW with your SCXI-1100 board, you do not need to read this chapter.
Programming Considerations
Programming the SCXI-1100 involves writing to the Configuration Register. Programming
Slot 0 involves writing to the HSCR and the FIFO Register. Programming the data acquisition
boards involves writes to their registers. See your data acquisition board user manual for more
information. The programming instructions list the sequence of steps to take. The instructions
are language independent; that is, they instruct you to write a value to a given register without
presenting the actual code.
Notation
For the bit patterns to be written, the following symbols are used:
0
Binary zero
1
Binary one
X
Don't care, either zero or one may be written
G
One of five bits used to specify the gain of the SCXI-1100. See the bit descriptions in the
Configuration Register section in Chapter 4, Register Descriptions, for more information.
C
One of five bits used to specify the channel to be loaded into the MUXCOUNTER. This
value is either the channel to be read for single reads, or a starting channel for scanned
measurements.
The 24-bit patterns are presented MSB first, left to right.
Register Writes
This section describes how to write to the Configuration Register, the HSCR, and the FIFO
Register, including the procedure for writing to the Slot-Select Register to select the appropriate
slot. For timing specifics, refer to the Communication Timing Requirements section in
Chapter 2, Configuration and Installation. Table 5-1 gives the rear signal connector pin
equivalences to the different National Instruments data acquisition boards. Also see Appendix E,
SCXI-1100 Cabling. The Configuration Register, the HSCR, and the FIFO Register are
write-only registers.
The different bits in these registers often control independent pieces of circuitry. There are times
when you may want to set or clear a specific bit or bits without affecting the remaining bits.
However, a write to one of these registers affects all bits simultaneously. You cannot read the
registers to determine which bits have been set or cleared in the past; therefore, maintain a
software copy of these registers. You can then read the software copy to determine the status of
the register. To change the state of a single bit without disturbing the remaining bits, set or clear
the bit in the software copy and write the software copy to the register.