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492 CHAPTER 11 /SYNCHRONOUS FSM DESIGN CONSIDERATIONS

a logic 1-0-1 (negative) glitch, as indicated by the following:

0-1-0 1-0-1
Positive (+) glitch Negative (-) glitch

As a voltage transient, an ORG may not develop to an extent that it crosses the switching
threshold of a next-stage device. Even so, the wise designer must expect that the ORG might
cross the switching threshold and take corrective measures to eliminate it.
By definition, a race condition is any state-to-state transition involving a change in two
or more state variables. Thus, race conditions do not exist between logically adjacent states.
The fact is that there are n! possible (alternative) race paths for state-to-state transitions
involving a change in n state variables. For example, a change in two state variables requires
two alternative race paths, while a change in three state variables allows for 3! = 6 alternative
race paths. But since the specific, real-time alternative race path that an FSM may take during
a state-to-state transition is not usually predictable, all possible alternative race paths must
be analyzed if corrective action is to be taken. It is on this premise that the following
discussion is based.
An ORG produced by a transition involving the change of two state variables is illustrated
in Fig. 11.la by a portion of a state diagram. Here, two race paths, associated with the
transition from state Oil to state 110, are indicated by dashed lines. One race path is by
way of race state 010 and the other via race state 111, a don't care state. Notice that the

Use <j> 7 as a 0 or X in Z
K-map else (+) glitch.
ABC Race path 2

Conditional
Branching

Destination
x
State

Race path 1
(a)
(+) Glitch
(b)
FIGURE 11.1
Illustration of an ORG caused by a transition from state 011 to state 110 involving a change in two
state variables, (a) Portion of a state diagram showing the two alternative race paths associated with
the transition, (b) Simplified diagram showing the origin and destination states, the race paths and
possible ORGs.