Digital Signal Processing Reference
In-Depth Information
Figure 17.9
These are the settings for the pushbutton PIO device to be added to the Nios II system.
17.7 Adding Parallel I/O Components
Many processors require a certain amount of general-purpose I/O pins. These
pins can be attached directly to pushbuttons, switches, LEDs, and similar I/O
devices. They can also be attached to relatively simple or low bandwidth
interfaces that don't have a large amount of overhead associated with data
transmission. Examples of these types of interfaces include PS/2, I
2
C, SPI, and
parallel data interfaces.
In addition, general-purpose I/O pins can be used to pass low-bandwidth data
between a custom VHDL or Verilog block and the Nios II processor. A faster
method of transferring data to a VHDL block is to create a custom peripheral
that can attach to the Avalon bus. Implementing a VHDL module that is
compliant with the Avalon bus specification is more involved and requires more
logic elements than using general-purpose I/O pins, but it does provide a faster
more efficient interface.
General-purpose I/O pins are added to the Nios II processor with the PIO
(Parallel I/O) component. The PIO component has a number of options for
customizing general-purpose I/O interfaces. PIO interfaces can be specified as
input only, output only, or bidirectional. If bidirectional is selected here, then
the direction of each pin must be set in the direction register at run-time via
software. Input PIO interfaces can also have various interrupt and edge capture
capabilities including the capturing of either or both edges and edge or level-
sensitive interrupt triggers.
