Adlink PCI-8554 Manual do Utilizador descarregar pdf (Página 43)

Signal Connection and Applications

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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)

1 2 ... 38 39 40 41 42 43 44 45 46 47 48 ... 66 67

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