LOGIC CIRCUIT DESIGN _II_

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					LOGIC CIRCUIT DESIGN (II)
   The problem is to design a logic
    circuit for TRAFFIC LIGHTS with
    two inputs A, B and three outputs
    R, Y, G.
TRAFFIC LIGHTS
   R, Y and G feed red, yellow and
    green lights (e.g. LEDs), these
    would flash in the order of Hong
    Kong traffic signals when A and B
    are supplied continuously by a two
    bit binary code representing
    numbers 0 to 3.
TRAFFIC LIGHTS

State   A   B   R   Y   G

 0      0   0

 1      0   1

 2      1   0

 3      1   1
TRAFFIC LIGHTS

State   A   B   R   Y   G

 0      0   0   1   0   0

 1      0   1   1   1   0

 2      1   0   0   0   1

 3      1   1   0   1   0
                      R = A B + A B

TRAFFIC LIGHTS        R = A (B + B)
                      R = A

State   A   B   R   Boolean Expression

 0      0   0   1        R=A B

 1      0   1   1        R=A B

 2      1   0   0        R=A B

 3      1   1   0        R=A B
                      Y = A B + A B

TRAFFIC LIGHTS        Y = B (A + A)
                      Y = B

State   A   B   Y   Boolean Expression

 0      0   0   0        Y=A B

 1      0   1   1        Y=A B

 2      1   0   0        Y=A B

 3      1   1   1        Y=A B
                      G = A B

TRAFFIC LIGHTS

State   A   B   G   Boolean Expression

 0      0   0   0        G=A B

 1      0   1   0        G=A B

 2      1   0   1        G=A B

 3      1   1   0        G=A B
TRAFFIC LIGHTS

 The Boolean expression of Traffic Lights

 R=A
 Y=B
 G = A.B
TRAFFIC LIGHTS

 The Logic Circuit of Traffic Lights

 R=A                A                  R
                    B                  Y
 Y=B
 G = A.B
                                       G
TRAFFIC LIGHTS
 Using NAND gates to implement the Boolean
 Expression.
                 A                       R
 R=A
                 B                      Y
 Y=B
 G = A.B
                                        G
Question

    The problem is to design a logic circuit for A
     COIN-OPERATED HOT DRINK MACHINE.
    It will provide a cup of tea or coffee under the
     following conditions.
Question

 The  conditions is ….
 (1) The correct amount of coin is inserted (P),_____

 (2) The cup is in position (Q), _____

 (3) The selector is set at “TEA”(T) ___ “COFFEE”(C)



 Please write down a Boolean expression for these
 conditions under which a drink (Z) can be provided and
 draw the logic circuit.
Question

 The  conditions is ….
                                                  AND
 (1) The correct amount of coin is inserted (P),_____
                                   AND
 (2) The cup is in position (Q), _____

 (3) The selector is set at “TEA”(T) OR “COFFEE”(C)
                                      ___

 Please write down a Boolean expression for these
 conditions under which a drink (Z) can be provided and
 draw the logic circuit.

				
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