ADLINK PCIe-7200 - Manual (Page 43)

34 Operation Theory
4.4 Handshaking
The 7200 series also supports a handshaking digital I/O transfer
mode. That is, after input data is ready, an I_REQ is sent from an
external device, and I_ACK will go high to acknowledge the data
already accessed.
I_REQ & I_ACK for Digital Input
1. Digital Input Data is ready.
2. An I_REQ signal is generated for digital input operation.
3. Digital input data is saved to FIFO.
4. An I_ACK signal is generated and sent to an outside
device.
5. If the FIFO is not empty and PCI bus is not occupied, the
data will be transferred to main memory.
Latch Digital Input
or Digital Output
Digital Input FIFO Bus mastering
DMA data Transfer
PC's Main Memory
2
4
3
1
Digital Input DATA
5
IN_REQ
IN_ACK