Data Translation DT9857, Руководство пользователя, Страница: 97 / 192

Principles of Operation
97
To select continuous edge-to-edge measurement mode, use software to specify the
counter/timer mode as continuous measure, the C/T clock source as internal, and the start
edge type.
Rate Generation
Use rate generation mode to generate a continuous pulse output signal from the counter’s
output line; this mode is sometimes referred to as continuous pulse output or pulse train
output. You can use this pulse output signal as an external clock to pace other operations, such
as analog input, analog output, or other counter/timer operations.
The pulse output operation is enabled whenever the counter’s gate signal is at the specified
level. While the pulse output operation is enabled, the counter outputs a pulse of the specified
type and frequency continuously. As soon as the operation is disabled, rate generation stops.
The period of the output pulse is determined by the C/T clock source (either internal using a
clock divider, or external). You can output pulses using a maximum frequency of 24 MHz (if
using the internal C/T clock) or 5 MHz (if using the external C/T clock). Refer to
page 93 for
more information about the C/T clock sources.
Note: The integrity of the signal degrades at frequencies greater than 10 MHz.
Using software, specify the counter/timer mode as rate generation (rate), the C/T clock
source as either internal or external, the clock divider (for an internal clock), the polarity of the
output pulses (high-to-low transition or low-to-high transition), the duty cycle of the output
pulses, and the active gate type (low-level or high-level). Refer to
page 94 for more
information about pulse output signals and to page 93 for more information about gate types.
Make sure that the signals are wired appropriately. Refer to page 58 for an example of
connecting a rate generation application.
One-Shot
Use one-shot mode to generate a single pulse output signal from the counter’s output line
when the specified edge is detected on the counter’s gate signal. You can use this pulse output
signal as an external digital (TTL) trigger to start other operations, such as analog input or
analog output operations.
After the single pulse is output, the one-shot operation stops. All subsequent clock input
signals and gate input signals are ignored.
The period of the output pulse is determined by the C/T clock source (either internal using a
clock divider, or external). Note that in one-shot mode, the internal C/T clock is more useful
than an external C/T clock; refer to
page 93 for more information about the C/T clock sources.