National Instruments 653X Manuale Utente

If you are performing a finite pattern output operation, you can call the DIO Wait VI 

instead of the DIO Write VI after the DIO Start VI. For more information about these VIs, 
see the LabVIEW Help.

By default, for output buffered transfers the 6534 device will preload the on 
board memory with data before starting the output operation. This is done 
to eliminate or reduce the impact of the PCI bus bandwidth limitations and 
increase the overall transfer rate. The preloading process will cause a small 
delay between the start command in software and the actual start of data 
transfer. If this is a concern, you may disable the preloading by calling the 
following function/VI before the software start command:

•

NI-DAQ C interface—In the 

Set_DAQ_Device_Info

 function, 

set the ND_FIFO_TRANSFER_COUNT to ND_NONE.

•

LabVIEW—In the DIO Parameter VI, set the Scarabs Preload Enable 
attribute to OFF.

You can configure your 653X device to acquire data whenever the state of 
one or more data lines change. Once the 653X device detects a change in 
one of the selected lines, it will capture data within 50–150 ns and outputs 
a pulse on the REQ pin. This mode increases CPU and bus efficiency 
because you can monitor activity on input lines without continuously 
polling or transferring unnecessary data during periods of inactivity.

The 653X device used alone will detect if a change occurred, but if used in 

conjunction with a 660X device (via a RTSI line), the relative time between changes can be 
acquired by the 660X device.

You can choose between a width of eight, 16, or 32 bits. Use the following 
table to find the valid combinations of ports and timing controllers you can 
use based on the width of data you want to acquire.

Table 2-4.  Port and Timing Controller Combinations

8 bits

Port 0 (DIOA<0..7>)

Group 1

Port 2 (DIOC<0..7>)

Group 2