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Computer Organization & Programming

Computer Organization & Programming. Chapter4 Combinatorial Components. Some common, useful combinatorial circuits. Multiplexor Some number (power of 2) of inputs and some control inputs

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Computer Organization & Programming

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  1. Computer Organization & Programming Chapter4 Combinatorial Components

  2. Some common, useful combinatorial circuits • Multiplexor • Some number (power of 2) of inputs and some control inputs • The current values on the control lines are interpreted as a binary representation of the number of one of the other inputs. That input is passed through to the output. • Demultiplexor • Reverse of the multiplexor • Single input is routed to one of a number (power of 2) output lines, depending on the control lines. • Decoder • Takes an n-bit input number and uses it to select exactly one of 2n output lines • note difference between demultiplexor and decoder • The selected output line will have a 1, not a selected input value. • Comparator • outputs a 1 if two input values are equal, 0 otherwise

  3. Comparator • All the As represent one input word, all the Bs represent another input word. The output will be one only if the two inputs are the same

  4. Mux (multiplexer) 2 -> 1

  5. Mux 2 -> 1 implementation

  6. Mux 4 -> 1

  7. Mux 8 -> 1 Abstract representation of a multiplexor. The circuit details are hidden, but the essentials are visible.

  8. Implement a Boolean Function using Mux

  9. Decoder 3->8

  10. Decoder circuit

  11. Decoder 4 -> 16

  12. Implement a Boolean Function using Decoder

  13. Shifter C determines if the shift will be left or right. Assume D = 10000110. Show exactly what passes through each gate, and what ends up in S.

  14. Half Adder Called a half adder because it does not do the whole job: it does not add a carry in.

  15. Full Adder

  16. Example – 4bit Adder

  17. Example – 4bit Adder/Subtractor

  18. ALU Slice

  19. 1bit ALU What happens if F= 11, A=1, B=1, carry in = 1 What happens if F= 10, A=1, B=1, carry in = 1 Note INVA (Inverse A), ENA (Enable A), ENB (Enable B) Once we have the circuit understood, note the inputs and the outputs. We can hide the rest of the details in using this device.

  20. 8Bit ALU

  21. Overflow

  22. ALU with overflow detection

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