Keithley KPCI-3110, Руководство пользователя

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KPCI-3110 and KPCI-3116 User’s Manual Functional Description 2-23
Figure 2-9
Counter/timer channel
C/T clock sources
The following clock sources are available for the user counters:
• Internal C/T clock
• External C/T clock
• Internally cascaded clock
Refer to the following subsections for more information on these clock sources.
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. The minimum frequency that
you can specify for the clock output signal is 305.18Hz.
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, 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 65,536. 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.
Clock Input Signal
(internal, external, or
internally cascaded)
Counter
Gate Input Signal
(software or
external input)
Pulse Output
Signal