Chapter 4
General-Purpose Counter/Timer
DAQ-STC Technical Reference Manual
4-2
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National Instruments Corporation
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Programmable input and output signal polarities
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One-shot, continuous, or tri-state output
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Two banks of dual-load registers that allow seamless frequency and duty cycle changes
during double-buffered pulse-train generation
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A counter load register that can increment or decrement on TC, which allows for
equivalent time sampling (ETS) timing output. ETS is a sampling method for repetitive
waveforms where the sample point is moved within the cycle. Refer to section
, for more information.
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Interevent (relative) time stamping
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Two sets of save registers to save the counter value via an external control signal or via
software command
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Current count value can be read without affecting circuit operation
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Bus interface support
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Interrupts based on TC or on active gate edge—rising edge, falling edge, or any edge
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Secondary interrupts to facilitate a DMA or local CPU interface for timing functions
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Not supported in hardware are BCD counting and time-of-day counting
4.3 Simplified Model
The GPCT module contains two identical 24-bit binary up/down counters—general-purpose
counters 0 and 1. Figure 4-1 shows a simplified model of the counter.
Figure 4-1.
General-Purpose Counter/Timer Simplified Model
G_UP_DOWN
G_SOURCE
G_GATE
INTERRUPT
G_OUT
Load Registers
24 Bit Up/Down Counter
Save Registers