Answers Database

Foundation: Difference between I/O Pads and I/O Terminals


Record #2140

Product Family:  Software

Product Line:  Aldec

Problem Title:
Foundation:  Difference between I/O Pads and I/O Terminals


Problem Description:
Keywords:  ipad opad iopad Terminal
Urgency:  Standard

General Description:
What is the difference between the I/O terminals found on
the toolbar in the Schematic Editor, and the I/O pads found
in the Xilinx libraries?


Solution 1:

I/O Terminals
-------------
These are placed by clicking on the I/O Terminal button on
the Toolbar on the left-hand side of the Schematic Editor
window.

I/O terminals should ONLY be used in macros to connect
signals to the corresponding pins on the macro symbol.
They provide the connection between levels of hierarchy
in the design.

If an I/O terminal is placed on a top-level schematic, it
MIGHT be treated as an I/O pad by the software.  But in
some cases, the terminal will not be treated as an I/O pad.
For this reason, I/O terminals should not be used on any
top-level schematic.  Signals that span multiple pages of
a flat design do not require terminals or off-page
connectors.


I/O Pads
--------
These are components from the Xilinx Unified Library, and
are placed just as you would add components like AND
gates, flip-flops, etc.  They are called IPAD, OPAD,
IOPAD, IPAD4, OPAD4, etc.

These may be used on any level of hierarchy.  They represent
the actual pins of the Xilinx device.  All device pins MUST
be represented with I/O Pads, not I/O Terminals.



End of Record #2140