National Instruments 653X Manuale Utente

the Data Overwrite/Regenerate parameter in the Digital Buffer Control VI, 
called by the DIO Start VI.

Similarly, with continuous output, the 653X device continuously reads 
data from computer memory. As the device retrieves data from the buffer, 
call the 

DIG_DB_Transfer

 function or the DIO Write VI to write the data. 

The device will stop and return an error if it runs out of data to output, but 
you have the option to allow it to regenerate data that has already been 
outputted. As in continuous input, you specify the device to allow 
regeneration with the oldDataStop parameter in the 

DIG_DB_Config

 

function and the data overwrite/regenerate parameter in the Digital Buffer 
Control VI, called by the DIO Start VI.

With 6534 devices, if you want to output the same block of data repeatedly, 
you have the option of loading a buffer of data into onboard memory and 
looping through this data block continuously. With this option, data is only 
transferred from computer memory to the device onboard memory once, 
and the device outputs the same block of data continuously from its 
onboard memory. This allows the device to output data at higher rates 
because it is not limited by the PCI bus bandwidth. To enable on-oard 
memory looping:

•

NI-DAQ C interface—Set the 

ND_PATTERN_GENERATION_LOOP_ENABLED

 to ND_ON in the 

Set_DAQ_Device_Info

 function.

•

LabVIEW—Set the Pattern Generation Loop Enable attribute to ON 
in the DIO Parameter VI.

When using DMA (by default), the 6534 device transfers data in 32-byte 
blocks and the 6533 device transfers data in 4-byte blocks. Therefore, at 
any time during a continuous operation, there may be up to 31 bytes (or 
3 bytes for 6533 devices) of data in an internal device FIFO. You can use 
interrupt driven transfers if you need to retrieve data immediately as it is 
acquired. Interrupt driven transfers are slower and take more processing 
time from the computer than DMA driven transfers.