National Instruments 321645c-01 User Manual

Page of 554
Chapter 2
Function Reference — CTR_Config
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 National Instruments Corporation
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NI-DAQ FRM for PC Compatibles
6:
Active high on gate of next higher-order counter.
7:
Active high on gate of next lower-order counter.
8:
Special gating.
outType selects which type of output is to be generated by the counter. The counters generate 
two types of output signals: TC toggled output and TC pulse output.
0:
TC toggled output type used.
1:
TC pulse output type used.
outPolarity selects the output polarity used by the counter.
0:
Positive logic output.
1:
Negative logic (inverted) output.
Using This Function
If you select TC pulse output type, outPolarity = 0 means that NI-DAQ generates active 
logic-high terminal count pulses. outPolarity = 1 means that NI-DAQ generates active 
logic-low terminal count pulses. Similarly, if you select TC toggled output type, then 
outPolarity = 0 means the OUT signal toggles from low to high on the first TC. outPolarity 
= 1 means the OUT signal toggles from high to low on the first TC.
CTR_Config
 saves the parameters in the configuration table for the specified counter. 
NI-DAQ uses this configuration table when the counter is set up for an event-counting, pulse 
output, or frequency output operation. You can use 
CTR_Config
 to take advantage of the 
many counter modes.
The default settings for the counter configuration modes are as follows:
edgeMode = 0: Counter counts rising edges.
gateMode = 0: No gating used.
outType = 0: TC toggled output type used.
outPolarity = 0: Positive logic output used.
To change the counter configuration from this default setting, you must call 
CTR_Config
 and 
indicate which configuration you want before initiating any other counter operation.
Counter configuration settings applied through this function persist when waveform 
generation functions use the same counter. For example, to externally trigger a waveform 
generation option, use this function to change the gatemode to 1 (high-level gating), and then 
call the waveform generation functions. The waveform generation is delayed until a 
high-level signal appears on the gate pin on the I/O connector. Notice that this is really not a 
trigger signal but is a gating signal, as the waveform generation pauses if the gate goes low at 
any time. Because the Am9513 counter/timer chip has certain limitations, you cannot use 
gateModes 3 and 4. You are responsible for producing a signal that stays high for the duration 
of the waveform generation operation.