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Chapter 2 Function Reference — GPCTR_Change_Parameter
©
National Instruments Corporation 2-201 NI-DAQ FRM for PC Compatibles
paramID = ND_START_TRIGGER (6602 and 455X devices only)
This
paramID
allows you to change how a counter arms itself. If
paramValue
is set to
ND_ENABLED
, the counter will be armed using a hardware arm. If
paramValue
is set to
ND_DISABLED
, the counter will be armed using a software arm.
ND_DISABLED
is the default
value.
You can synchronize the arming of multiple counters using a hardware signal. Counters must
be previously software armed before the hardware arm takes place. The hardware arming
circuitry looks for a rising edge on the hardware arming pin.
paramID =
ND_SOURCE_POLARITY
The general-purpose counter counts these the transitions of this the signal selected by
paramID
=
ND_SOURCE. ND_SOURCE
. Corresponding legal values for
paramValue
are
as follows:
•
ND_LOW_TO_HIGH
—counter counts the low-to-high transitions of the source signal
•
ND_HIGH_TO_LOW
—counter counts the high-to-low transitions of the source signal
paramID =
ND_PRESCALE_VALUE
(
6602 and 455
X
devices only)
This
paramID
specifies a prescaling to the counter source selection. Using this
paramID
allows the counter to measure frequencies higher than the normal counter-timer maximum.
Corresponding legal values for
paramValue
are as follows:
•
ND_ONE
—use this value if no prescaling is needed
•
ND_MAX_PRESCALE
—measures signals of a frequency that is an order of
ND_MAX_PRESCALE
higher than the maximum frequency supported by the 6602 and
455
X
counter-timers. The value of
ND_MAX_PRESCALE
can be queried using the
GPCTR_Watch
function call
paramID
=
ND_INPUT_CONDITIONING
(
6602 and 455
X
devices only)
The general-purpose counter enables the appropriate input conditioning on the default source
and up/down pins for the particular counter (see Table 2-23 and Table 2-29 for definitions of
the
default Source
and
Up/Down
pins). The
GPCTR_Change_Parameter
function with
paramID
=
ND_SOURCE
should not be called after a call to
GPCTR_Change_Parameter
with
paramID
=
ND_INPUT_CONDITIONING
. Corresponding legal values for
paramValue
are shown below:
•
ND_NONE
—
configures
default Source
and
Up/Down
pins for no conditioning
•
ND_QUADRATURE_ENCODER_X1
—configures
default Source
and
Up/Down
. Other
sources cannot be connected in this mode)
•
ND_QUADRATURE_ENCODER_X2
—configures
default Source
and
Up/Down
automatically. Other sources cannot be connected in this mode
•
ND_QUADRATURE_ENCODER_X4
—configures
default Source
and
Up/Down
automatically. Other sources cannot be connected in this mode
•
ND_TWO_PULSE_COUNTING
—configures
default Source
and
Up/Down
automatically.
Other sources cannot be connected in this mode