Chapter 5
Programming
© National Instruments Corporation
5-7
SCXI-1100 User Manual
Follow the instructions in these sections through the part labeled as follows:
• Clear the A/D circuitry and reset the mux counter in the MIO board user manual (except for
the AT-MIO-16X and AT-MIO-64F-5). Do not continue to the part called Enable the
scanning data acquisition operation until you program the modules and Slot 0.
• Program the sample counter (if you are doing continuous channel scanning) or Program the
scan-interval counter (if you are doing interval channel scanning) in the AT-MIO-16X and
AT-MIO-64F-5 user manuals. Do not continue to the part labeled Enable a scanning data
acquisition operation or Enable an interval scanning data acquisition operation until you
program the modules and Slot 0.
Note: For multiplexed scanning with an MIO board, it is important that you follow the
instructions in the channel scanning sections, not the single-channel sections. Although
you may be using only one MIO board channel, the channel scanning programming
ensures that the MIO board outputs SCANCLK, which the SCXI-1100 and Slot 0 need.
Counter 1 and SCANDIV
All MIO boards can operate their data acquisition board scan lists in two ways–they can acquire
one sample per data acquisition board scan list entry; or they can acquire N samples per data
acquisition board scan list entry, where N is a number from 2 to 65,535 that is programmed in
Counter 1. This second method of operation is especially useful when the data acquisition board
scan list length is limited to 16 entries, as it is on all MIO boards except the AT-MIO-16F-5,
AT-MIO-16X, and AT-MIO-64F-5, which can have up to 512 entries. Because you can
multiplex many SCXI-1100s in one chassis to one MIO board channel, often the simplest way to
program the MIO board is to use only one data acquisition board scan list entry, and make N the
total number of samples to be taken on all modules in one scan. Check your MIO board user
manual for limitations in the data acquisition board scan list format.
Because the SCXI-1100 has a fixed programmable gain, you may want to split up the samples
across data acquisition board scan list entries in order to use different gains of the MIO board.
For example, with the AT-MIO-16F-5, each sample can have its own gain entry. With the other
MIO boards, you can still group similar signals together and have, for example, the first five
readings at one MIO channel gain, the next five readings at another MIO gain, and so on.
Notice, however, that it is best to apply gain to a signal on the SCXI-1100 rather than to amplify
it later on the MIO board. Applying gain on the SCXI-1100 results in the SCXI chassis sending
a high-level signal, which is less susceptible to noise than a low-level signal, to the MIO board.
If you have different signals with greatly differing ranges, the best solution for reducing noise is
to use multiple SCXI-1100s with each module programmed for a gain best suited for the signals
the module is receiving.
To program the MIO board to take N samples per data acquisition board scan list entry, perform
the following additional programming steps at the end of the Enable the Scanning Data
Acquisition Operation, Enable a Scanning Data Acquisition Operation, or Enable an Interval
Scanning Data Acquisition Operation section in the appropriate data acquisition board user
manual:
1. Write FF01 to the Am9513 Command Register to select Counter 1 Mode Register.
2. Write 0325 (hex) to the Am9513 Data Register to store Counter 1 Mode Value for most MIO
boards. For the AT-MIO-16F-5, the AT-MIO-16X, and the AT-MIO-64F-5, write 1325
(hex).