ADLINK PCI-7300A - Manual (Page 45)

Operation Theory 33
4.3 Digital I/O Data Flow
When applying digital input functions, the data will be sampled into
the input FIFO periodically as we configured and then transfer to
the system memory by the bus mastering DMA of the PCI Bridge.
Figure 4-2 show the data flow of the 16-bit digital input operation.
Figure 4-2: Data flow of digital input
On the other hand, Figure 4-3 shows the data flow of 16-bit digital
output operation. After the bus mastering DMA of the PCI Bridge
transfers the output data to the output FIFO, the cPCI/PCI-7300A
will output the data to the external devices in a pre-assigned
period.
Figure 4-3: Data flow of digital output
The width of local data bus on the cPCI/PCI-7300A can be pro-
grammable to be 8-bit, 16-bit or 32-bit. The default data width is
16-bit. Port A is default to be input port, and Port B is default to be
output one. When 8-bit data width is applied, only the lower byte of
the bus will be used. While we program the data width to be 32-bit,
the two ports will operate in the same manner.