National Instruments 653X Manuale Utente

You can choose to send data from your 653X device to the peripheral 
device (output), or from the peripheral device to your 653X device (input).

In pattern I/O, the 653X device acquires/generates data on every falling or 
rising edge (programmable) of the REQ signal. The REQ signal can be 
generated internally or based on the clock of a peripheral device. An 
example of using external REQ is sharing a sample clock of an analog input 
device so you can synchronize the analog and digital operations.

By default, data from an external REQ source is transferred on the rising 
edge of the signal and on the falling edge of the internal REQ source. You 
can reverse the REQ polarity by using the following functions:

•

NI-DAQ C interface—Specify the REQ polarity in the 

DIG_Group_Mode

 function before calling the 

DIG_Block_PG_Config

 function.

•

LabVIEW—Specify the REQ polarity in the Digital Mode Config VI 
that is called by the DIO Config VI.

For more information on LabVIEW VIs and NI-DAQ functions, consult the 

LabVIEW Help and the NI-DAQ Function Reference Help.

Refer to Table C-1, 

, for an 

overview of all control/timing trigger lines.

If you are generating the REQ signal internally, you need to specify the rate 
of data transfer. The transfer rate is specified in software by using two 
parameters, the timebase frequency and timebase divisor:

where

timebase frequency = 20 MHz, 10 MHz, 1 MHz, 100 kHz, 10 kHz, 
1 kHz, or 100 Hz, and

timebase divisor = an integer between 1 and 65,355.