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ENEE 244 (01**). Spring 2006
Homework 5
Due back in class on Friday, April 28.
1. Fill up the function table (truth table) for the following latch. How is this latch related to those
described in the lectures and in the textbook? (Describe similarities and differences with the
most closely related latch).
2. The gated SR latch has unpredictable behavior if the S and R inputs are both equal to 1 when C
is 1. One way to solve this problem is to create a set−dominated gated SR latch in which the
condition S=R=1 causes the latch to be set to 1. Design a set−dominated gated SR latch. Show
the circuit. (Hint: Let the original circuit remain as it is, but add some external circuitry.)
3. A PN flip-flop has 4 operations: clear to 0, no change, complement, and set to 1, when inputs P
and N are 00,01,10, and 11, respectively. Tabulate its characteristic table (called the simplified
function table by the Givone text). Derive its characteristic equation.
4. Show how to implement a D flip−flop starting with a JK flip−flop.
5. A sequential circuit contains two flip-flops T1 and T2. The circuit has no external inputs. The
only external output are the values of the current state (Q1 and Q2). The flip-flop inputs are
connected as:
T1 = Q1 + Q2
T2 = Q1’ + Q2
Explain the intuitive function that the circuit performs.
6. A sequential circuit has two JK flip−flops with outputs Q1 and Q2 and one input x. The circuit
is described by the following flip−flop input equations:
J1 = x
J2= x
K1= Q2’
K2= Q1
a) Derive the next-state equations for the circuit.
b) Draw the state diagram.
