Intel® Quartus® Prime Pro Edition User Guide: Design Constraints

ID 683143
Date 10/04/2021

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3.2.3. Assigning Differential Pins

When you assign a differential I/O standard to a single-ended top-level pin in your design, the Pin Planner automatically recognizes the negative pin as part of the differential pin pair assignment and creates the negative pin for you. The Intel® Quartus® Prime software writes the location assignment for the negative pin to the .qsf; however, the I/O standard assignment is not added to the .qsf for the negative pin of the differential pair.

The following example shows a design with lvds_in top-level pin, to which you assign a differential I/O standard. The Pin Planner automatically creates the differential pin, lvds_in(n) to complete the differential pin pair.

Note: If you have a single-ended clock that feeds a PLL, assign the pin only to the positive clock pin of a differential pair in the target device. Single-ended pins that feed a PLL and are assigned to the negative clock pin device cause the design to not fit.
Figure 45. Creating a Differential Pin Pair in the Pin Planner

If your design contains a large bus that exceeds the pins available in a particular I/O bank, you can use edge location assignments to place the bus. Edge location assignments improve the circuit board routing ability of large buses, because they are close together near an edge. The following figure shows Intel device package edges.

Figure 46. Die View and Package View of the Four Edges on an Intel Device

When you assign differential pin pairs in Package View, a red connection line displays between the pair of differential pins. The Package View labels the positive and negative pins with the letters p and n, respectively.

Figure 47. Differential Pin Pair Color Coding

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