In order to maintain an acceptable noise level on the VCCIO supply, the Quartus® II software enforces restrictions on placement of single-ended I/O pads in relation to differential pads. Use the following guidelines for placing single-ended pads with respect to differential pads in Stratix® /Stratix GX and Cyclone® devices.
- Single-ended inputs may be only be placed four or more pads away from a differential pad.
- Single-ended outputs and bidirectional pads may only be placed five or more pads away from a differential pad.
The Quartus II software generates the error message for illegally placed pads.
Note: Altera® might relax this restriction in the future, pending silicon characterization. Please contact Altera Applications for more information.