When I implement an ECS schematic with a bus that is not fully connected (all bus bits have a driver, but not a load), the schematic check reports the following error:
"Error: Net 'net_name(xx)' must be connected to pins or I/O Ports."
This error is reported on each bit that is left unconnected.
In ISE 7.1i or later, a partial bus can be used as an I/O port with the use of Bus Renaming.
To use the Bus Renaming function:
1. Right-click an empty space in the schematic and select Object Properties.
2. Select Bus Renaming.
3. Select either "Only for Partial Bus IO" or "Always".
4. Select the desired Bus Renaming Format.
For internal buses, you can change these error messages into warnings as follows:
1. In ECS, select Edit -> Preferences.
2. Under "Schematic Editor/Check", change the "Consider Loadless Net as" and "Consider Undriven Net as" fields to "Warning" rather than "Error".
Alternatively, a buffer can be placed on the entire bus. Connect the input of a buffer component to the entire bus, and leave the output of the buffer unconnected.
NOTE: Using an iterative instance of a BUF component allows a buffer of any size. To create a buffer for a 5-bit bus, add a BUF component and rename the instance as "my5bitbuf(4:0)".