National Instruments AT-DIO-32F, User Manual

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Programming Chapter 4
AT-DIO-32F User Manual 4-50 © National Instruments Corporation
is a 10-MHz square wave. If the CNT1SRC bit is set, the counting source for Counter 1 is the
output of Counter 3. The same applies for Counter 2. The output of Counter 3 is programmed as
follows:
1. Set up Counter 3 for square wave generation by writing hex 96 to the CNTRCMD Register
for an 8-bit count or hex B6 for a 16-bit count.
2. Write the count to the CNTR3 Register (see Table 4-4). If the count is a 16-bit value, write
the least significant byte first, then the most significant.
The following equation is used to calculate the output frequency of Counter 3:
Counter 3 Output Frequency = 2000000 / data written to counter
Counters 1 and 2 can use either a 10-MHz clock or the output of Counter 3 as the counting
source. If the counting source is the 10-MHz square wave, then the following equation is used to
calculate the output frequency of the counter:
Counter 1, 2 Output Frequency = 10000000 / data written to counter
If the counting source is the output of Counter 3, then the following equation is used for
calculating the output frequency of the counter:
Counter 1, 2 Output Frequency = Counter 3 output frequency / data written to counter
Table 4-5. Counters 1 and 2 Programmable Frequency Output (Source = 10 MHz)
Data Written to CNTR1 Counter Output Frequency Pattern Interval
or CNTR2 (hex)
FFFF 152.0 Hz 6.58 msec
8000 305.0 Hz 3.28 msec
4000 610.0 Hz 1.67 msec
2000 1.22 kHz 820.0
µ
sec
FFF 2.44 kHz 410.0
µ
sec
A00 3.9 kHz 260.0
µ
sec
800 4.88 kHz 200.0
µ
sec
400 9.76 kHz 100.0
µ
sec
FF 39.0 kHz 25.6
µ
sec
A0 62.5 kHz 16.0
µ
sec
80 78.0 kHz 12.8
µ
sec
60 104.0 kHz 9.6
µ
sec
40 156.0 kHz 6.4
µ
sec
20 313.0 kHz 3.2
µ
sec
10 625.0 kHz 1.6
µ
sec
A 1.0 MHz 1.0
µ
sec
5 2.0 MHz 500.0 nsec
2 5.0 MHz 200.0 nsec