ADLINK PCIe-7300A - Manual (Page 64)

54 Operation Theory
As the data output in the internal clock mode, the DOREQ signal
could be use as the output strobe to indicate the output operation
to the external device. The timing diagram of the DOREQ is shown
as follows:
Figure 4-10: DOREQ as output data strobe
4.11.2 Digital Output DMA in Handshaking Mode
For digital output, through DO-REQ output signal and DO-ACK
input signal, the digital output can have simple handshaking data
transfer.