When tapping signals off a bus in Concept, unless you maintain the same name for the bits you tap off as the name of the parent bus, NGDBuild does not interpret the taps properly. For example, with a bus named “foo<2..0>”, the only allowed names of the bits tapped off of the bus are foo<2>, foo<1>, and foo<0>. Any deviation from these names requires that you insert a buffer between the bit tapped off the bus and the new name.
The typical error message issued by NGDBuild/EDIF2NGD for bits renamed in the process of tapping them off the bus follows.
Fatal_Error: Duplicate based:basedport.c port xx in cell alias_bitThe error indicates the programs considered that the bits tapped off the bus were renamed.
In the following figure, the bus taps, while legitimate configurations within Concept, do not process correctly by NGDBuild.
Figure 3.3 Unacceptable Bus Tap Naming For NGDBuild |  |
The next figure illustrates how to use angle brackets to modify the previous bus taps for use with NGDBuild.
Figure 3.4 One Correct Method of Creating NGDBuild-Legal Bus Taps | |
The next figure illustrates another unacceptable method for tapping three nets with different names into a bus. Although a valid method in Concept, NGDBuild does not process this configuration properly.
Figure 3.5 Unacceptable Bus Tap Naming | |
The next figure illustrates how you can modify the tapped bits of the bus in the by inserting a non-inverting buffer (BUFF) between the bus bit and the new name.
Figure 3.6 Another Correct Method of Creating NGDBuild-Legal Bus Taps | |
For information on how to set up bus taps, see the following sections in Chapter 3, “Creating a Design,” and the Cadence manual Concept Schematic User Guide.
