ADLINK PCIe-7300A - Manual (Page 66)

56 Operation Theory
The timing diagram of the DOREQ and DOACK in the DO hand-
shaking mode is shown as follows:
Figure 4-11: DOREQ & DOACK Handshaking
Note: DOACK must be deserted before DOREQ asserts, DOACK
can be asserted any time after DOREQ asserts, DOREQ will
be reasserted after DOACK is asserted.
4.11.3 Digital Output DMA in Burst Handshaking Mode
The burst handshaking mode is a fast and reliable data transfer
protocol. It has both advantage of handshaking mode, which is
reliable, and the advantage of internal clock mode, which is fast.
When using this mode, the sender has to check the availability of
receiver indicated by the DO-ACK signal before it starts to send
data. Once the DO-ACK is asserted, the receiver has to keep the
DO-ACK signal asserted before its input buffer becomes too small.
When the DO-ACK is de-asserted, indicating the receiver’s buffer
has not much space for new data, the sender is still allowed to
send 4 data to the receiver, and the receiver has to receive these
data. The following figure illustrates the operation of the burst
handshaking mode: