ADLINK PCI-8554 - Manual (Page 43)

Signal Connection and Applications • 33
4.4.2 To generate a 1 pulse/1 hour signal
Step 1: Use a fixed clock source because the output is a fixed
frequency.
Step 2: As the desired frequency is too slow, one counter will
be unable to produce the desired frequency
(1/3600sec=0.000278Hz. Therefore to reach this low
frequency, cascade the independent counters 1, 2
and 3. Set the clock source of counter 1 to the
internal 8MHz. Connect COUT1 to clock source of
counter 2, and connect COUT2 to clock source of
counter 3.
Step 3: Using the counter divider function, set counter 1 to
4000, counter 2 to 2000, and counter 3 to 3600.
∴ 8MHz/4000/2000/3600 = 1/3600,
Hence COUT3 will generate a pulse every hour.
Step 4: The gate sources to enable always, hence GATE1,
GATE2, and GATE3 are open.
Step 5: Write and verify the control program. Refer to
‘DEMO2.C’ source code.
COUT1
Counter #1
8254 Chip #1
'H'
ECK1
GND
CK1
COUT10
8MHz
COUT11
set by function "8554_SET_cntCLK"
set by function
"_8554_SET_CK1"
COUT2
Counter #2
8254 Chip #1
'H'
set by function "8554_SET_cntCLK"
ECK2
COUT1
CK1
COUT10
COUT3
Counter #3
8254 Chip #1
'H'
ECK3
COUT2
CK1
COUT10
set by function "8554_SET_cntCLK"
Figure 21: Example of frequency generator (2)