murali_vml,
There are two common buffer overflow and overwrite errors.
Overflow error -10845 occurs when the NI-DAQ driver cannot read data from the DAQ device's FIFO buffer fast enough to keep up with the acquired data as it flows to the buffer (i.e., the FIFO buffer overflows before all the original data can be read from it). This is usually due to limitations of your computer system, most commonly the result of slow processor speeds (< 200 MHz) in conjunction with PCMCIA DAQ boards, which have small FIFO buffers (e.g., the DAQCard-500). Sometimes using a DAQCard with a larger FIFO can solve the problem, but a better solution is to lower the acquisition rate or move to a faster system. Another cause of the -10845 error could be due to an interrupt-driven
acquisition. For example, PCMCIA bus does not support Direct Memory Access (DMA). If the system is tied up processing another interrupt (like performing a screen refresh or responding to a mouse movement) when it is time to move data from the board, then that data may get overwritten.
Overwrite error -10846 occurs when the data in the software buffer that you created for an analog input operation gets overwritten by new data before you can retrieve the existing data from the buffer. This problem can be solved by adjusting the parameters of your data acquisition, such as the lowering the scan rate, increasing the buffer size, and/or increasing the number of scans to read from the buffer on each buffer read. Additionally, performing less processing in the loop can help avoid the -10846 error.
See the NI-DAQ Function Reference Manual for a listing of all NI-DAQ error codes.
Have a great day.
