Measurement Computing Data Translation DT9857, Руководство пользователя

Страница: 94 / 192

Chapter 5
94
• Rising-edge external gate input – Enables a counter/timer operation when a low-to-high
transition is detected on the counter’s gate signal. In software, this is called a high-edge
gate type. Note that this gate type is used for edge-to-edge measurement, one-shot, and
repetitive one-shot mode; refer to
page 94 for more information about these modes.
Specify the gate type in software.
Pulse Output Types and Duty Cycles
DT9857 and DT9857E modules can output the following types of pulses from each
counter/timer:
• High-to-low transitions – The low portion of the total pulse output period is the active
portion of the counter/timer clock output signal.
• Low-to-high transitions – The high portion of the total pulse output period is the active
portion of the counter/timer pulse output signal.
You specify the pulse output type in software.
The duty cycle (or pulse width) indicates the percentage of the total pulse output period that is
active. For example, a duty cycle of 50 indicates that half of the total pulse output is low and
half of the total pulse output is high. You specify the duty cycle in software.
Figure 35 illustrates a low-to-high pulse with a duty cycle of approximately 30%.
Figure 35: Example of a Low-to-High Pulse Output Type
Counter/Timer Operation Modes
Counters on the DT9857 and DT9857E module support the following counter/timer operation
modes:
• Event counting
• Up/down counting
• Edge-to-edge measurement
• Continuous edge-to-edge measurement
• Rate generation
Total Pulse Period
Active Pulse Width
low pulse
high pulse