National Instruments AT-MIO-16D, User Manual, Page: 158 / 291

Programming Chapter 4
AT-MIO-16D User Manual 4-66 © National Instruments Corporation
4. Program the scan-interval counter.
Use Counter 2 of the Am9513A Counter/Timer as the scan-interval counter. Counter 2 can be
programmed to generate a pulse once every N counts. N is referred to as the scan interval, that is,
the time between successive scan sequences programmed into the mux-gain memory. N can be
between 2 and 65,536. One count is equal to the period of the timebase clock used by the
counter. The following clocks are available internal to the Am9513A–1 MHz, 100 kHz, 10 kHz,
1 kHz, and 100 Hz. In addition, the scan-interval timer can use signals connected to any of the
Am9513A SOURCE input pins.
To program the scan-interval counter, use the following programming sequence. All writes are
16-bit operations. All values given are hexadecimal.
a. Write FF02 to the Am9513A Command Register to select the Counter 2 Mode Register.
b. Write the mode value to the Am9513A Data Register to store the Counter 2 mode value. Use
one of the following mode values:
8B25 – Selects 1-MHz clock
8C25 – Selects 100-kHz clock
8D25
– Selects 10-kHz clock
8E25 – Selects 1-kHz clock
8F25 – Selects 100-Hz clock
8525 – Selects signal at SOURCE5 input as clock (counts the rising edge of the signal,
6 MHz maximum)
c. Write FF0A to the Am9513A Command Register to select the Counter 2 Load Register.
d. Write 2 to the Am9513A Data Register to store the Counter 2 load value.
e. Write FF42 to the Am9513A Command Register to load Counter 2.
f. Write FFF2 to the Am9513A Command Register to step Counter 2 down to one.
g. Entries stored in the mux-gain memory should be scanned once during a scan interval. The
following condition must be satisfied:
scan interval
≥
sample interval * x, where x is the number of entries in the scan sequence.
Write the desired scan interval to the Am9513A Data Register to store the Counter 2 load
value:
• If the scan interval is between 2 and FFFF (65,535 decimal), write the scan interval to the
Am9513A Data Register.
• If the scan interval is 10000 (65,536 decimal), write 0 to the Am9513A Data Register.
h. Write FF22 to the Am9513A Command Register to arm Counter 2.
After you complete this programming sequence, Counter 2 is configured to assign a time interval
to scan sequences once the trigger to enable A/D conversions is detected.