Tutorial: ITI1100

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Tutorial ITI1100

• Dewan Tanvir Ahmed
• SITE, UofO

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General Decoder Diagram
Decoders

• Decoder - logic circuit that activates an output
  that corresponds to a binary number on the input
  (set of inputs).

Demo
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Decoder

• A n-to-m decoder
• a binary code of n bits 2n distinct information
• n input variables up to 2n output lines
• only one output can be active (high) at any time

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Three-line-to 8-line (or 1-of-8) decoder
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Decoder (cont..)

• Expansion
• two 3-to-8 decoder a 4-to-16 deocder
• a 5-to-32 decoder?

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Decoder (cont..)

• each output a minterm
• use a decoder and an external OR gate to
  implement any Boolean function of n input
  variables
• A full-adder
• S(x,y,x)S(1,2,4,7)
• C(x,y,z) S(3,5,6,7)

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Lab-3
Something like this
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BCD to 7-Segment DisplayDesign Requirements
Design the logic circuitry that will drive a
seven segment LED display and will be able to
represent numbers from 0 to 9
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Possible numbers and their representation on 7
segment display
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Truth Table
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Signal b implementation
X1X0 00 01 11 10
X3X2 00 01 11 10
00 1  1  1   1 
01 1 0 1    0 
11 X     X X X
10  1   1  X  X  
b f(X3, X2, X1, X0)
X1X0
X1X0
X2
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Signal c implementation
X1X0 00 01 11 10
X3X2 00 01 11 10
00 1  1  1   0 
01 1 1 1    1 
11 X     X X X
10  1   1  X  X  
c f(X3, X2, X1, X0)
X1
X0
X2
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7 segment display

• All the anode segments are connected together
• Power must be applied externally to the anode
  connection that is common to all the segments
• By applying the ground to a particular segment
  (i.e. a,b,g etc..), the appropriate segment will
  light up

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7 segment common anode

• A resistor should be added in order to limit the
  current through LED
• The current to light the active LED is sink by
  the logic component, which is preferable

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7 segment display

• All the cathode of the LED are connected together
• The common connection must be grounded and power
  must be applied to appropriate segment in order
  to illuminate that segment
• The current to light the active LED is generated
  by the logic component, which generates the logic
  1

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BCD to 7 Segment Decoder/Drivers

• Common-anode requires VCC , LED ON when Output
  is LOW.
• Common-cathode NO VCC , LED ON when Output is
  HIGH.
• TTL and CMOS devices are normally not used to
  drive the common-cathode display directly because
  of current (mA) requirement. A buffer circuit is
  used between the decoder chips and common-cathode
  display

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7447 TTL IC

• Real world example of BCD to 7 segment decoder
• Outputs of the decoder are active low and a
  common anode 7 segment display is used

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Lab BCD to 7 Segment Decoder/Drivers

• (a) BCD-to-7-segment decoder/driver driving a
  common-anode 7-segment LED display
• (b) segment patterns for all possible input codes.

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Multiplexers (Data Selectors)

• A multiplexer (MUX) selects one of multiple input
  signals and passes it to the output.
• The basic two input multiplexer
• The four input multiplexer
• The eight input multiplexer

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Multiplexers (Data Selectors)

• A multiplexer (MUX) selects 1 out of N input data
  sources and transmits the selected data to a
  single output

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Multiplexers Two-input multiplexer
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Multiplexers Four-input multiplexer
Four-input multiplexer - using sum of products
logic
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Multiplexers Eight-input multiplexer The 74151
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Multiplexers Eight-input multiplexer
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Multiplexers (cont..)
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Boolean function implementation

• MUX a decoder an OR gate
• 2n-to-1 MUX can implement any Boolean function of
  n input variable
• a better solution implement any Boolean function
  of n1 input variable
• n of these variables the selection lines
• the remaining variable the inputs

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Multiplexers (cont..)

• Example F(A,B,C)S(1,3,5,6)

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Multiplexers (cont..)

• Procedure
• assign an ordering sequence of the input variable
• the leftmost variable (A) will be used for the
  input lines
• assign the remaining n-1 variables to the
  selection lines w.r.t. their corresponding
  sequence
• list all the minterms in two rows (A' and A)
• circle all the minterms of the function
• determine the input lines

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Multiplexers (cont..)

• An example F(A,B,C,D)S(0,1,3,4,8,9,15)

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Exercise

• Try to build an inverter using 2-1 MUX
• Try to build XOR gate using 4-1 MUX

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Lab Multiplexers
Four-input multiplexer - using sum of products
logic
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Thank You!