DAQ VXI-SC-1102 Manual de Instruções descarregar pdf (Página 52)

Chapter 7 PC-TIO-10 Timing I/O Device

National Instruments Corporation 7-3 DAQ Hardware Overview Guide

• High-Level Gate N–1 Gating—the counter is active when the gate

input of the next lower-order counter is at high-logic state. Otherwise,

the counter is suspended.

Counter operation starts and stops relative to the selected timebase. When

you configure a counter for no gating, the counter starts at the first

timebase/source edge (rising or falling, depending on the selection) after

the software configures the counter. When you configure a counter for

gating modes, gate signals take effect at the next timebase/source edge. For

example, if you configure a counter to count rising edges and to use the

falling edge gating mode, the counter starts counting on the next rising edge

after it receives a high-to-low edge on its GATE input. Thus, some time is

spent synchronizing the GATE input with the timebase/source. This

synchronization time creates a time lapse uncertainty from zero to one

timebase period between the application of the signal at the GATE input

and the start of the counter operation.

The counter generates timing signals at its OUT output. If the counter is not

operating, you can set its output to one of three states—high-impedance

state, low-logic state, or high-logic state.

The counters generate two types of output signals during counter operation:

TC pulse output and TC toggled output. A counter reaches TC when it

counts up (to 65,535) or down (to 0) and rolls over. In many counter

applications, the counter reloads from an internal register when it reaches

TC. In TC pulse output mode, the counter generates a pulse during the cycle

in which it reaches TC. In TC toggled output mode, the counter output

changes state on the next source edge after reaching TC. In addition, you

can configure the counters for positive logic output or negative (inverted)

logic output. Figure 7-2 shows examples of the four types of output signals

generated.

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DAQ VXI-SC-1102 Manual de Instruções Página 52