Verilog® HDL: A Guide to Digital Design and Synthesis, Second Edition

Appendix A. Strength Modeling and Advanced Net Definitions

Strength Levels

Verilog allows signals to have logic values and strength values. Logic values are 0, 1, x, and z. Logic strength values are used to resolve combinations of multiple signals and to represent behavior of actual hardware elements as accurately as possible. Several logic strengths are available. Table A-1 shows the strength levels for signals. Driving strengths are used for signal values that are driven on a net. Storage strengths are used to model charge storage in trireg type nets, which are discussed later in this appendix.

Table A-1. Strength Levels

Strength Level	Abbreviation	Degree	Strength Type
supply1	Su1	strongest 1	driving
strong1	St1	driving
pull1	Pu1	driving
large1	La1	storage
weak1 ...