National Instruments 320682C CounterMeasureFrequency

Chapter 10 Easy I/O for DAQ Library

sourceEdge is the edge of the counter source or timebase signal on which it increments, and this

parameter accepts the following attributes:

• COUNT_ON_RISING_EDGE

• COUNT_ON_FALLING_EDGE

gateMode specifies how the signal on the counter's GATE pin is used. The options are:

• UNGATED_SOFTWARE_START—ignore the gate signal and start when CounterStart is

called.

• COUNT_WHILE_GATE_HIGH—count while the gate signal is TTL high after

CounterStart is called.

• COUNT_WHILE_GATE_LOW—count while the gate signal is TTL low after

CounterStart is called.

• START_COUNTING_ON_RISING_EDGE—start counting on the rising edge of the TTL

gate signal after CounterStart is called.

• START_COUNTING_ON_FALLING_EDGE—start counting on the falling edge of the TTL

gate signal after CounterStart is called.

CounterMeasureFrequency

short error = CounterMeasureFrequency (short device, char counter[],

unsigned short counterSize,

double gateWidthSampleTimeinSec,

double maxDelayBeforeGateSec,

unsigned short counterMinus1GateMode,

double *actualGateWidthSec,

short *overflow, short *valid,

short *timeout, double *frequency);

Purpose

Measures the frequency of a TTL signal on the specified counter's SOURCE pin by counting

rising edges of the signal during a specified period of time. In addition to this connection, you

must also wire the counter's GATE pin to the OUT pin of counter-1. For a specified Counter,

Counter-1 and Counter+1 are defined as shown in Table 10-4.