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Chapter 2 Function Reference — GPCTR_Change_Parameter
©
National Instruments Corporation 2-207 NI-DAQ FRM for PC Compatibles
Software Control
This function lets you customize the counter for your application. You can use this function
after the
GPCTR_Set_Application function, and before GPCTR_Control function with
action =
ND_PREPARE or action = ND_PROGRAM. You can call this function as many times as
you need to.
The software up or down control is available by default; if you do not use the
GPCTR_Change_Parameter function with paramID set to ND_UP_DOWN, the counter is
configured for the software up or down control and starts counting up. To make the counter
use the software up or down control and start counting down, use the
GPCTR_Change_Parameter function with the paramID set to ND_UP_DOWN and the
paramValue set to
ND_COUNT_DOWN. To change the counting direction during counting, use
the
GPCTR_Control function with the action set to ND_COUNT_UP or ND_COUNT_DOWN.
Hardware Control
To use hardware to control the counting direction, use I/O connector lines as shown in
Table 2-29; the counter will count down when the I/O line is in the low state and up when it
is in the high state. Use the
GPCTR_Change_Parameter function with the paramID set to
ND_UP_DOWN and the paramValue set to ND_HARDWARE to take advantage of this counter
feature.
paramID = ND_BUFFER_MODE (6602 and 455X devices only)
Corresponding legal values for paramValue are shown below:
•
ND_SINGLE
for single buffer operations.
•
ND_DOUBLE for continuous buffer operation.
Table 2-29.
Default Up/Down Selection
gpctrNum E Series Devices 6602 Devices 455X Devices
ND_COUNTER_0
Digital I/O Line 6
ND_PFI_37 ND_PFI_29
ND_COUNTER_1
Digital I/O Line 7
ND_PFI_33 ND_PFI_25
ND_COUNTER_2
N/A
ND_PFI_29
N/A
ND_COUNTER_3
N/A
ND_PFI_25
N/A
ND_COUNTER_4
N/A
ND_PFI_21
N/A
ND_COUNTER_5
N/A
ND_PFI_17
N/A
ND_COUNTER_6
N/A
ND_PFI_13
N/A
ND_COUNTER_7
N/A
ND_PFI_9
N/A