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Unformatted text preview: uations from the maps. Section 15.6 (p. 484) 1. Assign flipflop state values to correspond to the states in the
reduced table.
2. Construct a transition table which gives the next states of the
flipflops as a function of the present states and inputs. 3. Derive the nextstate maps from the transition table. Figure 159a: Next State Maps for Table 156. Table 156
X 4. Find flipflop input
maps from the nextstate
maps using the
techniques developed in
Unit 12 and find the flipflop input equations from
the maps. Figure 159b: Next State Maps for
Table 156 Table 157:
Represents a
sequential circuit with
two inputs (X1 and X2)
and two outputs (Z1
and Z2). Figure 1510: Next State Maps for
Table 157 Figure 1511: Derivation of SR Equations for Table 157 Equivalent State Assignments
After state minimization => assign flipflop states to
correspond to the states in the table. Given a sequential circuit with three states and two flipflops (A and B), there are 4 × 3 × 2 = 24 possible state
assignments for the three states. The logic required to realize a sequential design depends
on the way this state assignment is made.
Table 158. State Assignments for 3Row Tables Section 15.7 (p. 487) If flop has both Q and Q' as outputs ("symmetrical"),
complementing one or more columns of a state
assignment will have no effect on the cost of realization. Note: if asymmetrical flipflops are used (e.g., a D flipflop), complementing a column may require adding an
inverter to the circuit.
Figure 1512: Equivalent Circuits Obtained by
Complementing Qk Table 159. Figure 1513: Equivalent Circuits Obtained by
Complementing Qk When realizing threestate sequential circuit with
symmetrical flipflops, it is only necessary to try three
different states to be assured of a minimum cost realization.
Similarly, only three different assignments must be tried for
four states. A3 and B3 differ in col order, C3 is complement of A3
JK FlipFlops
Assignment A
J1 = X Q2'; K1 = X'; J2 = X Q1'; K2 = X; Z = X' Q1 + X Q2;
Assignment B
J2 = X Q1'; K2 = X'; K1 = X; K1 = X Q2; Z = X' Q2 + X Q1;
Assignment C
K1 = X Q2; J1 = x'; K2 = X' Q1'; J2= X; Z = X' Q1' + X Q2‘; D flipflops
Assignment A
D1 = X Q2'; D2 = X Q1';
Assignment B
D1 = X' + Q2'; D2 = X'(Q1+ Q2);
Assignment C
D1 = X'(Q2 + Q1); D2 = X + Q1 Q2...
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This document was uploaded on 03/16/2014 for the course EE 316 at University of Texas at Austin.
 Spring '08
 Brown

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