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692 CHAPTER 14 / ASYNCHRONOUS STATE MACHINE DESIGN AND ANALYSIS

External
Inputs
Sanity

T
(IT) Indicates a holding condition
v /
CUT if S -
^ * Indicates a transition path
(a) (b)
FIGURE 14.6
The FSM in Figs. 11.42 and 11.43 interpreted as an asynchronous FSM to be operated in the funda-
mental mode, (a) State diagram, (b) State table.

indicate FSM instability according to Eq. (14.4). Perhaps the most important use of state
tables is in the designs of FSMs without the use of K-maps. This will be demonstrated later
in connection with the design of STT machines.

14.6 DESIGN OF THE BASIC CELLS BY USING THE LPD MODEL

The reader who is familiar with Section 10.4 will recall that the set-dominant basic cell
and the reset-dominant basic cell were developed by a heuristic approach. This was done to
avoid having to use asynchronous design methods which, at that time, would have caused
unnecessary delays in the primary goals of that chapter. Now, it is appropriate that the basic
memory cells be designed from first principles by using the LPD model. The basic cells
represent two of the simplest asynchronous FSMs that are operated in the fundamental mode.

14.6.1 The Set-Dominant Basic Cell
The state diagram for the set-dominant basic cell is shown in Fig. 14.7a and is a reproduction
of that given in Fig. 10.12a. The NS logic for this basic cell is easily found by using the
mapping algorithm, given in Section 10.6, to combine information contained in the state
diagram with that contained in the excitation table for the LPD model in Fig. 14.7b. The result