Chapter 4
General-Purpose Counter/Timer
DAQ-STC Technical Reference Manual
4-72
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National Instruments Corporation
4.8.10.4 TC Latency Error
This error indicates that some programming action related to the TC was not performed in
time. In several functions (for example, buffered pulse-train generation with software
programming) the software performs some action on the counter while the counter is running,
and the action must complete before the counter TC is reached. If the counter TC is reached
before the software is able to confirm the programming (see Gi_TC_Interrupt_Ack), then the
TC latency error is set.
4.8.11 Detailed Operation by Application
This section discusses the detailed operation of the counter for the GPCT applications.
Each description begins with a summary of how you program the counter to implement the
application. A short paragraph then describes the operation of the internal signals. Finally,
a figure shows the explicit relationship between applied signals and internal signals for the
application.
The G_SOURCE signal is generated differently depending on whether you select internal
timing or external timing. When you select internal timing, G_SOURCE is simply the internal
source clock. When you select external timing, the active edge of the external source
generates both edges of G_SOURCE—first, the falling edge, then the rising edge. A delay
gate determines the width of the G_SOURCE negative pulse. Figure 4-31 shows the
relationship between G_SOURCE and the source clock for internal and external timing.
Figure 4-31.
G_SOURCE Generation
4.8.11.1 Simple Event Counting
In simple event counting, the counter increments on every G_SOURCE rising edge following
the ARM. To read the counter contents, use the save register.
Internal Source
G_SOURCE
External Source
G_SOURCE
Internal
External
