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Chapter 2 Function Reference — GPCTR_Change_Parameter
NI-DAQ FRM for PC Compatibles 2-206
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National Instruments Corporation
paramID =
ND_COUNT_1, ND_COUNT_2, ND_COUNT_3, ND_COUNT_4
The general-purpose counter uses these numbers for pulse width specifications when the
counter is configured for one of the simple pulse and pulse train generation applications. For
example, when you use the counter for FSK,
ND_COUNT_1
and
ND_COUNT_2
specify the
duration of low and high output states for one gate state and
ND_COUNT_3
and
ND_COUNT_4
specify them for the other gate state. Corresponding legal values for
paramValue
are shown
in Table 2-28.
For the 6602 devices, you can call
GPCTR_Change_Parameter
with
paramID
=
ND_COUNT_1
or
ND_COUNT_2
after arming the counter with a
GPCTR_Control
call. By using this, you can modify the duty cycle of a pulse-train whose generation was
started by the
GPCTR_Set_Application
call with
application
=
ND_PULSE_TRAIN_GNR
.
You can generate a pulse train with seamless frequency by using this methodology. After
modifying the
ND_COUNT_1
and
ND_COUNT_2
you should call
GPCTR_Control
with
action
=
ND_SWITCH_CYCLE
to activate the new duty cycle.
paramID =
ND_AUTOINCREMENT_COUNT
The value specified by
ND_COUNT_1
is incremented by the value selected by
ND_AUTOINCREMENT_COUNT
every time the counter is reloaded with the value specified
by
ND_COUNT_1
.
For example, with this feature you can generate retriggerable delayed pulses with
incrementally increasing delays. You can then use these pulses for applications such as
equivalent time sampling (ETS). Corresponding legal values for
paramValue
are 0
through 2
8
– 1.
paramID =
ND_UP_DOWN
When the application is
ND_SIMPLE_EVENT_CNT
or
ND_BUFFERED_EVENT_CNT
, you can
use the up or down control options of the DAQ-STC general-purpose counters. You can use
the up or down control options for other counter applications, too. Software or hardware can
perform the up or down control.
Table 2-27.
Legal Values for
paramValue
when
paramID
=
ND_INITIAL_COUNT
E Series and 445X Devices 6602 and 455X Devices
0 through 2
24
– 1 0 through 2
32
– 1
Table 2-28.
Legal Values for
paramValue
when
paramID
=
ND_COUNT_1
,
ND_COUNT_2
,
ND_COUNT_3
, and
ND_COUNT_4
E Series and 445X Devices 6602 and 455X Devices
0 through 2
24
– 1 0 through 2
32
– 1