NuDAQ PCI-8554, User Manual, Page: 41 / 62

Signal Connection and Applications
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4.4 Frequency Generator
Example 1: To generate a 250 K Hz Square Wave.
step 1: To use fixed clock source because the output is a fixed
frequency.
step 2: I nternal 8M Hz is suitable to generate 250K Hz frequency.
Use Counter #1 for this application.
250 KHz = 8 M Hz / 32
step 3: Skip these steps.
step 4: The gate source is enable always, so let SCCI-II connector
pin99 GATE1 open
step 5: Connect the counter output to external device and write the
control program. Please refer the ‘DEMO1.C’ source code.
COUT1
Counter #1
8254 Chip #1
C
G
O
'H'
ECK1
GND
CK1
COUT10
8MHz
COUT11
set by function "8554_SET_cntCLK"
set by function
"_8554_SET_CK1"
Figure 4.2 Example of frequency generator (1)
Example 2: To generate a very low frequency of 1 pulse / 1 hour
step 1: To use fixed clock source because the output is a fixed
frequency.
step 2: Because the desired frequency (1/3600sec=0.000278Hz)
is too slow to use one counter to generate, set the
independent counter #1 & #2 & #3 to cascade mode: Clock
source of counter #1 comes from
C8M , clock source of
counter #2 comes from COUT1, clock source of counter #3
comes from COUT2. Divider value of counter #1 was set to
4000, divider value of counter #2 was set to 2000, divider
value of counter #3 was set to 3600,
8MHz /4000/2000/3600
= 1/3600, so COUT3 will generate a pulse every hour.
step 3: Skip these steps.
step 4: The gate source is enable always, so let
GATE1 GATE2
GATE3 open.
step 5: Write and verify the control program. Please refer the
‘DEMO2.C’ source code.