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418 CHAPTER 9 / PROPAGATION DELAY AND TIMING DEFECTS

(a) Construct an LPDD for this function (exactly as written) and find the hazard cover
for each of the static hazards and the conditions required to produce the dynamic
hazard. Indicate the initial and final states for each of the static hazards. Follow
the example in Fig. 9.16. (Hint: No dynamic hazard exists due to a change in
either input A or D, and the one that does exist is conditional on A. Also, look for
the possibility that a static hazard may change from a static 1-hazard to a static
0-hazard depending on the order of change of one or two variables.)
(b) Use a BDD to show the enabling paths of the variable whose change is responsible
for the dynamic hazard formation. Follow the example in Fig. 9.18.
(c) Use a timing diagram (simulation) to show the development of the dynamic hazard.
Demonstrate that the dynamic hazard cannot be eliminated by adding static hazard
cover.
(d) Demonstrate with both an LPDD and a timing diagram that the dynamic hazard
can be eliminated by making the B paths to the output less asymmetric.

9.13 At the discretion of the instructor, use the EXL-Sim2002 simulator included on the
CD-ROM bundled with this text to simulate any of the following problems: 9.3b,
9.4b, 9.6b, 9.1 Ib, 9.12c, 9.12d. For example, an assignment 9.13/9.6(b) requires the
use of EXL-Sim2002 to verify the existence of the static 1-hazard and its hazard cover
by simulating the five variable function Z in Fig. P9.2.