ADLINK Technology NuDAQ ACL-8454, User Manual

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Applications
4.4 Frequency Measurement
Example : To measure frequency around 1~100 K Hz
step 1: This application need two counters. One counter is used to
generate a pulse whose time interval is very precise. The
pulse is used to enable the other counter (counting counter)
by gate control. On ACL-8454, internal gate control is
possible. The internal gate is coming from /COUT6. In this
example, the pulse generate is counter #6 and the counter
#1 is used to measure frequency.
step 2: The maximum value of counting counter is no more than
65535, For measuring 100 K Hz frequency, the time interval
should be within 1/100 K Hz x 65535 = 0.655 sec. If the time
interval is wider then the measurement resolution is better,
however, if time interval is too long the counting value will be
overflow. That means the low pulse width of counter #6
output should shorter than 0.655 sec. User can try to
generate the pulse by counter #6 by yourself.
step 3: Configur jumper ‘CK1’. The clock source is the signal to be
measured.
step 4~6: Skip these steps.
step 7: Set the internal jumper ‘G1’. The gate is controlled
internally.
step 8: The following block diagram illustrates the application
step 9: Write and verify the control program. The frequency of the
signal is :
frequency = counting value of counter #1 / precise time interval
Please refer the ‘DEMO4.C’ source code.
COUT5
COUT6
Counter #6
8254 Chip #2
C
G
O
'H'
COUT1
Counter #1
8254 Chip #1
C
G
O
Jumper
CK1
/COUT6
frequency to
be measured
Precise
Time
Interval
'H' enable counter #1
Jumper
G1