Keithley KPCI-3101 Series, Руководство пользователя

Страница: 39 / 146

KPCI-3101 — KPCI-3104 Series User’s Manual Principles of Operation 2-19
Counter/Timer features
The counter/timer circuitry on the board provides the clocking circuitry used by the A/D sub-
system as well as several user counter/timer features. This section describes the following user
counter/timer features:
•
Counter/timer channels
• C/T clock sources
•
Gate types
• Pulse types and duty cycles
•
Counter/timer operation modes
Counter/Timer channels
The KPCI-3101–4 Series board supports four user 16-bit counter/timer channels (called
counters); counters are numbered 0, 1, 2, and 3.
Figure 2-8
Counter/Timer channel
Each counter corresponds to a counter/timer (C/T) subsystem. To specify the counter to use in
software, specify the appropriate C/T subsystem. For example, counter 0 corresponds to C/T
subsystem element 0; counter 3 corresponds to C/T subsystem element 3.
Using software, you can internally route the clock output signal from one user counter to the
clock input signal of the next user counter to internally cascade the counters. In this way, you
can create a 32-bit counter without externally connecting two counters together.
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.
Clock Input SIgnal
(internal, external, or
internally cascaded)
Counter
Gate Input Signal
(software or
external input)
Pulse Output
Signal