ADLINK PCI-7300A - Manual (Page 54)

42 Operation Theory
The operation flow is show as below:
Note: When the DMA function of digital input starts, the input data
will be stored in the FIFO of the cPCI/PCI-7300A. The data
then transfer to system memory if PCI bus is available. If the
speed of translation from external device to the FIFO on
board is higher than that from FIFO to system memory or the
PCI bus is busy for a long time, the FIFO become full and
overrun situation occurs after the next data being written to
the input FIFO. Users should check the overrun status to see
whether the overrun occurs or not. Some input data will lost
when the input FIFO is overrun.
The overrun occurs when the DMA idle time (from the end of
DMA transfer N to the start of DMA transfer N+1) is longer