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C++BOLD Reference Manual

16.2. Naming Conventions for Ports

Port names are typically entirely uppercase.

Active-low ports should have names that end in _N (underscore N).

16.2.1. No-connect Pins

If a part contains any no-connect or do-not-connect pins, these pins should all be declared in a single port named NC. This allows all such pins for all parts in a module to be connected to the global no-connect net with the following statement:

wireall( "/NC", "NC" );

16.2.2. Bus Ports

For bus ports, the preferred range order is H:L. E.g., D[31:0] is preferred to D[0:31]. By default, the pt_to_h Support Tool automatically forces port ranges to use the H:L ordering convention.

16.2.3. Differential Pairs

Differential pairs may be represented as either two separate ports or a single bus port. If two ports are used, they should have identical names, except the last two characters, which should be _P (underscore P, for the positive signal) and _N (underscore N, for the negative signal).

The recommended convention for busses of differential pairs is for all pairs to be included in a single bus, with the positive signals having even indexes and the negative signals having corresponding odd indexes.

For example, sixteen differential pairs may be represented as a single 32-wide port.

This convention works well with FPGA's, for which the functionality of I/O may not be set at the time of board-level design. For example, if the convention is always followed, and two FPGA's are connected together via a bus, the FPGA designer can readily identify differential pairs regardless of the width of the bus.