TNM identifiers define symbols or groups of symbols that are used in timing specifications. They can also define other groups. The following figure shows an example of a TNM attribute attached to an individual symbol. In this circuit, the flip-flop D_FF has the attribute TNM=D_FF attached to it.
Figure 4.19 Example of Using TNMs and TIMEGRPs in Your Schematic |  |
The TIMEGRP symbol contains an attribute that defines a group of flip-flops called Q_FFS, which includes all flip-flops in the schematic except the one labeled D_FF. You can then use the group Q_FFS to create timing specifications in the TIMESPEC primitive. The flip-flop D_FF has its clock enable driven at 1/2 of the clock frequency; therefore, its flip-flop to pad and pad to flip-flop timing specifications are longer than the flip-flop to pad specifications in the Q_FFS group.
