Digital I/O
How to use the PCI-6534 onboard memory ?
![Tom_W_[DE]](http://forums.ni.com/attachments/ni/130/2061/1/mean_robot.jpg "Tom_W_[DE]"){kind=avatar}
Hi MES-
There can actually be significant differences between programming for a 6534 versus the essentially FIFO-less 6533. The last post in this thread was from 5 years ago and discussed the Traditional (Legacy) NI-DAQ driver, so let's assume now that you're using the newer NI-DAQmx driver.
The existence of deep onboard memory (aka SCARAB) on the 6534 means that you can operate at the full speed of the device for a much longer period of time than with a 6533. This is true for a few reasons. First, as the original response indicated, in the case of a continuous double-buffered operation, the onboard FIFO will be used to buffer samples if there is no PCI bus bandwidth available at the time. This is a significant advantage over the 6533 because the 16 sample buffer on that device will overflow quickly when using a high acquisition rate if the bus becomes temporarily unavailable. This advantage will be handled seamlessly by the NI-DAQmx driver, just as the Traditional NI-DAQ driver would have done previously.
In the case of a finite acquisition less than 32Msamples you can make use of the FIFO to acquire all samples onto the card independently of PCI bus activity and then later transfer the data across after the time-critical acquisition period. This behavior is controlled by adjusting the DAQmx Channel Property "Data Transfer Request Condition" to only transfer samples from the board's FIFO when an acquisition has completed. This is done in C using the "DAQmxSetDIDataXferReqCond(TaskHandle taskHandle, const char channel[], int32 data);" property, or in LabVIEW as shown here:
Hopefully this helps-
There can actually be significant differences between programming for a 6534 versus the essentially FIFO-less 6533. The last post in this thread was from 5 years ago and discussed the Traditional (Legacy) NI-DAQ driver, so let's assume now that you're using the newer NI-DAQmx driver.
The existence of deep onboard memory (aka SCARAB) on the 6534 means that you can operate at the full speed of the device for a much longer period of time than with a 6533. This is true for a few reasons. First, as the original response indicated, in the case of a continuous double-buffered operation, the onboard FIFO will be used to buffer samples if there is no PCI bus bandwidth available at the time. This is a significant advantage over the 6533 because the 16 sample buffer on that device will overflow quickly when using a high acquisition rate if the bus becomes temporarily unavailable. This advantage will be handled seamlessly by the NI-DAQmx driver, just as the Traditional NI-DAQ driver would have done previously.
In the case of a finite acquisition less than 32Msamples you can make use of the FIFO to acquire all samples onto the card independently of PCI bus activity and then later transfer the data across after the time-critical acquisition period. This behavior is controlled by adjusting the DAQmx Channel Property "Data Transfer Request Condition" to only transfer samples from the board's FIFO when an acquisition has completed. This is done in C using the "DAQmxSetDIDataXferReqCond(TaskHandle taskHandle, const char channel[], int32 data);" property, or in LabVIEW as shown here:
Hopefully this helps-
Message Edited by Tom W [DE] on 02-14-2006 08:46 PM
