lecture 6 universal gates
DESCRIPTION
Digital Logic : Universal GatesTRANSCRIPT
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Universal Gates
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Review of Boolean algebra
• Just like Boolean logic• Variables can only be 1 or 0
– Instead of true / false
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Review of Boolean algebra• Not is a horizontal bar above the number
– 0 = 1– 1 = 0
• Or is a plus– 0+0 = 0– 0+1 = 1– 1+0 = 1– 1+1 = 1
• And is multiplication– 0*0 = 0– 0*1 = 0– 1*0 = 0– 1*1 = 1
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Basic logic gates
• NOT
• AND
• OR
• NAND
• NOR
• XOR
x x
xy
xy xyxyz
zx+yx
yxy
x+y+zz
xy
xy
x+yxy
xÅyxy
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Universal Gate – NANDThis presentation will demonstrate• The basic function of the NAND gate.• How a NAND gate can be used to replace an AND gate, an OR
gate, or an INVERTER gate.• How a logic circuit implemented with AOI(And, OR, Inverter)
logic gates can be re-implemented using only NAND gates.• That using a single gate type, in this case NAND, will reduce
the number of integrated circuits (IC) required to implement a logic circuit.
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AOI Logic NAND Logic
More ICs = More $$ Less ICs = Less $$
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NAND Gate
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X Y Z0 0 1
0 1 1
1 0 1
1 1 0
XY
Y X YXZ +
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NAND Gate as an Inverter Gate
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X Z0 1
1 0
X XZ
XXX (Before Bubble)
Equivalent to Inverter
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NAND Gate as an AND Gate
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X Y Z0 0 0
0 1 0
1 0 0
1 1 1
XY
YX YXZ
YX
NAND Gate Inverter
Equivalent to AND Gate
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NAND Gate as an OR Gate
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X Y Z0 0 0
0 1 1
1 0 1
1 1 1
Equivalent to OR Gate
X
YYXY X Y XZ ++
X
NAND GateInverters
Y
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NAND Gate Equivalent to AOI Gates
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INVERTERORAND
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Process for NAND Implementation1. If starting from a logic expression, implement the design with
AOI logic.
2. In the AOI implementation, identify and replace every AND,OR, and INVERTER gate with its NAND equivalent.
3. Redraw the circuit.
4. Identify and eliminate any double inversions (i.e., back-to-back inverters).
5. Redraw the final circuit.
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NAND Implementation
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Example:Design a NAND Logic Circuit that is equivalent to the AOI circuit shown below.
CA C B +
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NAND Implementation
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Solution – Step 2
Identify and replace every AND,OR, and INVERTER gate with its NAND equivalent.
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NAND Implementation
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Redraw the circuit.
Solution – Step 3
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NAND Implementation
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Identify and eliminate any double inversions.
Solution – Step 4
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NAND Implementation
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Solution – Step 5
Redraw the circuit.
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Proof of Equivalence
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C C B
C AC A C BZ
C AC BZ
CA C B
+
+
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AOI vs. NAND
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IC Type Gates Gate / IC # ICs
74LS04 1 6 1
74LS08 2 4 1
74LS32 1 4 1
Total Number of ICs → 3
IC Type Gates Gate / IC # ICs
74LS00 4 4 1
Total Number of ICs → 1
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Universal Gate – NORThis presentation will demonstrate…• The basic function of the NOR gate.• How an NOR gate can be using to replace an AND gate, an OR
gate or an INVERTER gate.• How a logic circuit implemented with AOI logic gates could be
re-implemented using only NOR gates• That using a single gate type, in this case NOR, will reduce the
number of integrated circuits (IC) required to implement a logic circuit.
AOI Logic NOR Logic
More ICs = More $$ Less ICs = Less $$ 19
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NOR Gate
X Y Z0 0 1
0 1 0
1 0 0
1 1 0
XY
Y X Y XZ +
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NOR Gate as an Inverter Gate
X Z0 1
1 0
X XZ
XXX + (Before Bubble)
Equivalent to Inverter
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NOR Gate as an OR Gate
X Y Z0 0 0
0 1 1
1 0 1
1 1 1
XY
YX Y XZ ++
Y X +
NOR Gate “Inverter”
Equivalent to OR Gate
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NOR Gate as an AND Gate
X Y Z0 0 0
0 1 0
1 0 0
1 1 1
Equivalent to AND Gate
X
YY XY X Y XZ +
X
NOR Gate“Inverters”
Y
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NOR Gate Equivalent of AOI Gates
INVERTERORAND
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Process for NOR Implementation1. If starting from a logic expression, implement the design with
AOI logic.
2. In the AOI implementation, identify and replace every AND,OR, and INVERTER gate with its NOR equivalent.
3. Redraw the circuit.
4. Identify and eliminate any double inversions. (i.e. back-to-back inverters)
5. Redraw the final circuit.
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NOR ImplementationExample:
Design a NOR Logic Circuit that is equivalent to the AOI circuit shown below.
CA C B +
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NOR ImplementationSolution – Step 2
Identify and replace every AND,OR, and INVERTER gate with its NAND equivalent.
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NOR ImplementationRedraw Circuit.
Solution – Step 3
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NOR ImplementationIdentify and eliminate any double inversions.
Solution – Step 4
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NOR ImplementationSolution – Step 5
Redraw Circuit.
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Proof of Equivalence
B
CA C AC A +
C A C BZ
C A C B
+
+
C
C
A
C BC BCB +
C A C B +
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AOI vs NOR
IC Type Gates Gate / IC # ICs
74LS04 1 6 1
74LS08 2 4 1
74LS32 1 4 1
Total Number of ICs → 3
IC Type Gates Gate / IC # ICs
74LS02 7 4 2
Total Number of ICs → 2
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