National Instruments SCXI-1120 User Manual page 82

Chapter 5
To program the hardscan circuitry, perform the following steps:
1. Write binary 0000 0000 to the HSCR.
2. Write binary 0000 1000 to the HSCR.
3. Write the Slot 0 scan list to the FIFO.
4. Write binary 0010 1100 to the HSCR.
5. Write binary 101S 1100 to the HSCR.
6. Write binary 101S 1110 to the HSCR.
7. Write binary 101S 1111 to the HSCR.
To program the hardscan circuitry to use the current scan list, perform the following steps:
1. Write binary 0000 1000 to the HSCR.
2. Write binary 0100 1000 to the HSCR.
3. Write binary 0000 1000 to the HSCR.
4. Write binary 0010 1100 to the HSCR.
5. Write binary 101S 1100 to the HSCR.
6. Write binary 101S 1110 to the HSCR.
7. Write binary 101S 1111 to the HSCR.
In the preceding steps:
S = 0 if you want the scanning to repeat when the end of the list is reached.
S = 1 if you want the circuitry to shut down after a single scan.
When you are writing multiple entries to the same register, for example, repetitive writes to the
HSCR or several FIFO entries, it is important that SS*13 or SS*14 go inactive (high) between
each entry. Select another slot or toggle the SLOT0SEL* line to temporarily deassert the
appropriate SS* line.
If consecutive scan list entries access an SCXI-1120, the module will reload the
MUXCOUNTER with the starting channel after each entry. Thus, two entries with counts of
four for one module will yield different behavior than one entry with a count of eight.
For multiple-chassis scanning, program each Slot 0 with dummy entries to fill the sample counts
when the data acquisition board is accessing other chassis. Use Slot 13 as the dummy entry slot.
See Example 3 at the end of this chapter.
© National Instruments Corporation 5-11
Programming
SCXI-1120 User Manual