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Tutorial: ITI1100

Tutorial: ITI1100. Dewan Tanvir Ahmed SITE, UofO. General Decoder Diagram. Decoders. Decoder - logic circuit that activates an output that corresponds to a binary number on the input (set of inputs). Demo. Decoder. A n-to-m decoder a binary code of n bits = 2 n distinct information

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Tutorial: ITI1100

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  1. Tutorial: ITI1100 Dewan Tanvir Ahmed SITE, UofO

  2. General Decoder Diagram Decoders Decoder - logic circuit that activates an output that corresponds to a binary number on the input (set of inputs). Demo

  3. Decoder • A n-to-m decoder • a binary code of n bits = 2ndistinct information • n input variables; up to 2noutput lines • only one output can be active (high) at any time

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

  5. Decoder (cont..) • Expansion • two 3-to-8 decoder: a 4-to-16 deocder • a 5-to-32 decoder?

  6. 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)

  7. Lab-3 Something like this:

  8. 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

  9. Possible numbers and their representation on 7 segment display

  10. Truth Table

  11. Signal b implementation b = f(X3, X2, X1, X0) = X1’X0’ + X1X0 + X2’

  12. Signal c implementation c = f(X3, X2, X1, X0) = X1’+ + X0 + X2

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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.

  19. 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

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

  21. MultiplexersTwo-input multiplexer

  22. MultiplexersFour-input multiplexer Four-input multiplexer - using sum of products logic

  23. MultiplexersEight-input multiplexer: The 74151

  24. MultiplexersEight-input multiplexer

  25. Multiplexers (cont..)

  26. 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 n+1 input variable • n of these variables: the selection lines • the remaining variable: the inputs

  27. Multiplexers (cont..) • Example: F(A,B,C)=S(1,3,5,6)

  28. 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

  29. Multiplexers (cont..) • An example: F(A,B,C,D)=S(0,1,3,4,8,9,15)

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

  31. Lab: Multiplexers Four-input multiplexer - using sum of products logic

  32. Thank You!

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