module 7
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Module 7. Hardware. Introduction. Switches are the basic blocks of computer hardware. We build increasingly complex hardware from these simple switches. An example of a switch that we use everyday in our lives is the Light Switch. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
Module 7
Hardware
Introduction
• Switches are the basic blocks of computer hardware.
• We build increasingly complex hardware from these simple switches.
• An example of a switch that we use everyday in our lives is the Light Switch.
Introduction
• The switches that we use in computer hardware are far too small to be seen by the naked eye.
• Then how are these components constructed if they are that small?
Introduction
• The answer rests in three technologies:
Introduction
• The answer rests in three technologies:– The idea of representing information by electrical
signals which led to development of the telegraph. • Switching devices developed such as Vacuum tubes,
but they all suffered from the disadvantages of being large, high power consumption and slow speed.
Introduction
• The answer rests in three technologies:– The idea of representing information by electrical
signals which led to development of the telegraph. • Switching devices developed such as Vacuum tubes,
but they all suffered from the disadvantages of being large, high power consumption and slow speed.
– Invention of transistor which is a very small switch.
Introduction• The answer rests in three technologies:– The idea of representing information by electrical
signals which led to development of the telegraph. • Switching devices developed such as Vacuum tubes, but
they all suffered from the disadvantages of being large, high power consumption and slow speed.
– Invention of transistor which is a very small switch.– Photography.
• The computer scientists got the idea of having layers of chemicals on top of each other from photography to “print” the wires of circuit directly on a non-conducting base and this led to invention of Integrated Circuits (ICs) which packs thousands of transistors on one chip.
Electrical Switches
• We adopt the convention that:
Electrical Switches
• We adopt the convention that:– A high voltage in a wire is represented by the symbol 1.– Little or no voltage in a wire represented by symbol 0.
Electrical Switches
• We adopt the convention that:– A high voltage in a wire is represented by the symbol 1.– Little or no voltage in a wire represented by symbol 0.
• With this convention a switch can be viewed as a logic operator.
Electrical Switches
• We adopt the convention that:– A high voltage in a wire is represented by the symbol 1.– Little or no voltage in a wire represented by symbol 0.
• With this convention a switch can be viewed as a logic operator.
• Think of a switch as box with three wires connected to it called in, out and control.
Electrical Switches
• We adopt the convention that:– A high voltage in a wire is represented by the symbol 1.– Little or no voltage in a wire represented by symbol 0.
• With this convention a switch can be viewed as a logic operator.
• Think of a switch as box with three wires connected to it called in, out and control.
• Our switches will come in two basic varieties:
Electrical Switches
• We adopt the convention that:– A high voltage in a wire is represented by the symbol 1.– Little or no voltage in a wire represented by symbol 0.
• With this convention a switch can be viewed as a logic operator.
• Think of a switch as box with three wires connected to it called in, out and control.
• Our switches will come in two basic varieties: – Normally open– Normally closed
An electronic switch in general
Normally Open Switch
• In a normally open switch, current can pass from in to out only when there is a signal at the control wire.
Normally Open Switch
• In a normally open switch, current can pass from in to out only when there is a signal at the control wire.
• That is when control is 1.
Normally Open Switch
• In a normally open switch, current can pass from in to out only when there is a signal at the control wire.
• That is when control is 1.• Otherwise the value of out is 0.
Normally Open Switch
Normally Closed Switch
• In a normally close switch, current can pass from in to out unless there is a signal at the control wire.
Normally Closed Switch
• In a normally close switch, current can pass from in to out unless there is a signal at the control wire.
• That is when control is 0.
Normally Closed Switch
• In a normally close switch, current can pass from in to out unless there is a signal at the control wire.
• That is when control is 0.• Otherwise the value of out is 0.
Normally Closed Switch
Logic
• From computer science perspective we are not concerned with electrical currents and voltages.
Logic
• From computer science perspective we are not concerned with electrical currents and voltages.
• We adopted the convention that:
Logic
• From computer science perspective we are not concerned with electrical currents and voltages.
• We adopted the convention that:– A high voltage in a wire is represented by the symbol 1.– Little or no voltage in a wire represented by symbol 0.
Logic
• From computer science perspective we are not concerned with electrical currents and voltages.
• We adopted the convention that:– A high voltage in a wire is represented by the symbol 1.– Little or no voltage in a wire represented by symbol 0.
• With this convention a switch can be viewed as a logic operator.
Logic
• From computer science perspective we are not concerned with electrical currents and voltages.
• We adopted the convention that:– A high voltage in a wire is represented by the symbol 1.– Little or no voltage in a wire represented by symbol 0.
• With this convention a switch can be viewed as a logic operator.
• We can regard a switch as an operator that produces an output state depending only on the input states.
Logic
• Example: S = John and Merry are happy. P = John is happy. Q = Merry is happy. S = P AND Q .
Logic
• Example: S = John and Merry are happy. P = John is happy. Q = Merry is happy. S = P AND Q . • AND is a logical operator.• We refer to P and Q as components of logical
operator AND.
Logic
• Suppose we decide to interpret – 0 as false.– 1 as true.
Logic
• Suppose we decide to interpret – 0 as false.– 1 as true.
• Then the action of normally open switch is the same, under this interpretation, as that of AND logical operator.
Logic
• Suppose we decide to interpret – 0 as false.– 1 as true.
• Then the action of normally open switch is the same, under this interpretation, as that of AND logical operator.
• Logical AND operator is evaluated to true if and only if both of its operands are true.
Logic
• A normally open switch acts as an AND operator.
• We refer to it as an AND gate. It has three components:– two input lines.– one output line.
AND Gate
AND Gate
OR gate
• OR is another logical operator. We also have a gate for OR and we call it OR gate.
OR gate
• OR is another logical operator. We also have a gate for OR and we call it OR gate.
• An OR gate like AND gate has three components:– Two input lines– One output line
OR gate
• OR is another logical operator. We also have a gate for OR and we call it OR gate.
• An OR gate like AND gate has three components:– Two input lines– One output line
• A Logical OR operator evaluates as true if at least one of the operands are true.
OR gate
• OR is another logical operator. We also have a gate for OR and we call it OR gate.
• An OR gate like AND gate has three components:– Two input lines– One output line
• A Logical OR operator evaluates as true if at least one of the operands are true.
• In the same line, an OR gate has output 1 if at least one of the input lines are 1.
OR Gate
NOT Gate• We have logical operator NOT which reverses
the truth value of its statement. Ex: R = Peter is happy. then, NOT R = Peter is not happy.
NOT Gate• We have logical operator NOT which reverses the truth value
of its statement. Ex: R = Peter is happy. then, NOT R = Peter is not happy.• As two other logical operator we have a corresponding NOT
gate which has two components:– One input line– One output line
NOT gate
Logical Expressions
• We can use the three basic logical operators, AND, NOT and OR to build any logical expression by combining them.
EX: We have two named statements: P = Button A has been pushed. R = Button B has been pushed. We want to write an expression Q which is true when either both of the buttons have been pushed or none of them.
Example
P R Q
1 1 1
1 0 0
0 1 0
0 0 1
True = 1False = 0P = 1 means button A has been pushed.
Finding the appropriate Expression
P R PR P’ R’ P’R’ PR + P’R’
1 1 1 0 0 0 1
1 0 0 0 1 0 0
0 1 0 1 0 0 0
0 0 0 1 1 1 1
PR stands for P AND RP’ stands for NOT PM + N stands for M OR NThus, we have Q = PR + P’R’
Building a Logical Circuit
• Now we want to build the a circuit for our computer using AND, OR and NOT gates which corresponds to logical expression Q = PR + P’R’
• That is given inputs P and R (in 0 and 1) produces Q (in 0 and 1)
Big Picture
Step 1
Step 2
Step 2
Step 3
Step 3
Multiplexer
• A multi-way switch• A two way multiplexer has two input lines,
one select line and one output line.• The select line determines the current from
which input line should pass to output line.
Multiplexer
2-way MUXa b select output
1 1 1 1
1 1 0 1
1 0 1 1
1 0 0 0
0 1 1 0
0 1 0 1
0 0 1 0
0 0 0 0
2-way MUX
• Select input a if the select is 1.• Select input b if the select is 0.
2-way MUX
Decoder
• Decoder is a circuit which has a single input and multiple outputs. It has one or more select lines.
• Select lines determine the current of input line should pass to which of the output lines.
Decoder
Two-way Decoder
a s0 x1 x0
1 1 1 0
1 0 0 1
0 1 0 0
0 0 0 0