National Instruments 653X - Manual (Page 35)

Chapter 2 Using Your 653X
© National Instruments Corporation 2-17 653X User Manual
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.
Generating and Receiving Digital Patterns and
Waveforms—Pattern I/O
Using pattern I/O, you can acquire or generate patterns on every rising or
falling edge of a clock signal. The clock signal can be generated internally
by an onboard 32-bit counter set to a user-specified frequency or the clock
signal can be received from the REQ pin in the I/O connector.
Note Feed external clocking signals into the PCLK pin for burst-mode handshaking and
into the REQ pin when performing pattern I/O.
Deciding the Width of Data to Transfer
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 transfer.
Table 2-3. Port and Timing Controller Combinations
Transfer
Width
Possible Port
Combinations
Timing Controllers
That Can Be Used
8 bits Port 0 (DIOA<0..7>) Group 1
Port 2 (DIOC<0..7>) Group 2
16 bits Port 0, Port 1 Group 1
Port 2, Port 3 Group 2
32 bits Port 0, Port 1, Port 2, Port 3 Group 1