Keithley KPCI-3101 Series, Руководство пользователя

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2-20 Principles of Operation KPCI-3101 — KPCI-3104 Series User’s Manual
Internal C/T clock
The internal C/T clock uses a 20MHz time base. Counter/timer operations start on the rising
edge of the clock input signal.
Through software, specify the clock source as internal and the frequency at which to pace the
counter/timer operation (this is the frequency of the clock output signal). The maximum fre-
quency that you can specify for the clock output signal is 10MHz. For a 16-bit counter, the min-
imum frequency that you can specify for the clock output signal is 305.17Hz. For a 32-bit
cascaded counter, the minimum frequency that you can specify for the clock output signal is
0.00465Hz, which corresponds to a rate of once every 215 seconds.
External C/T clock
The external C/T clock is useful when you want to pace counter/timer operations at rates not
available with the internal C/T clock or if you want to pace at uneven intervals. The rising edge
of the external C/T clock input signal is the active edge.
Using DriverLINX software, specify the clock source as external and the clock divider used to
determine the frequency at which to pace the operation (this is the frequency of the clock output
signal). The minimum clock divider that you can specify is 2.0; the maximum clock divider that
you can specify is 65535. For example, if you supply an external C/T clock with a frequency of
5MHz and specify a clock divider of 5, the resulting frequency of the external C/T clock output
signal is 1MHz. The resulting frequency of the external C/T clock output signal must not exceed
2.5MHz.
Connect the external C/T clock source to the board through the STA-300 screw terminal panel as
follows:
•
For Counter 0, connect the external C/T clock signal to screw terminal TB26 (pin 41 of
connector J1)
• For Counter 1, connect the external C/T clock signal to screw terminal TB30 (pin 7 of
connector J1)
•
For Counter 2, connect the external C/T clock signal to screw terminal TB34 (pin 36 of
connector J1)
• For Counter 3, connect the external C/T clock signal to screw terminal TB38 (pin 2 of
connector J1)
Internally cascaded clock
The KPCI-3101–4 Series board supports internal cascading on counters 0 and 1, 1 and 2, and 2
and 3. Cascading counters internally is an effective way to create a 32-bit counter without exter-
nally connecting two counters together.
To specify internal cascading, use DriverLINX software to set the internal cascade mode, then
specify the clock input and gate input for the first counter in the cascaded pair. Specify the clock
source of the second counter as C/T
N–1
. The clock output signal from first counter is the clock
input signal of the second counter. For example, if counters 1 and 2 are cascaded, specify the
clock input and gate input for counter 1.
The rising edge of the clock input signal is active.