cs2100-7-MSI

cs2100-7-MSI - CS2100Computer Organisation MSI...

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CS2100 Computer  Organisation http://www.comp.nus.edu.sg/~cs2100/ MSI Components (AY2009/2010) Semester 2
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CS2100 MSI Components 2 WHERE ARE WE NOW? Number systems and codes Boolean algebra Logic gates and circuits Simplification Combinational circuits Sequential circuits Performance Assembly language The processor: Datapath and control Pipelining Memory hierarchy: Cache Input/output Preparation: 2 weeks Logic Design: 3 weeks Computer organisation
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CS2100 MSI Components 3 MSI COMPONENTS Introduction Decoders Encoders Demultiplexers Multiplexers
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CS2100 MSI Components 4 INTRODUCTION Four common and useful MSI circuits: Decoder Demultiplexer Encoder Multiplexer Block-level outlines of MSI circuits: decoder code entity encoder code entity mux data input select demux data output select
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CS2100 MSI Components 5 DECODERS (1/5) Codes are frequently used to represent entities, eg: your name is a code to denote yourself (an entity!). These codes can be identified (or decoded) using a decoder. Given a code, identify the entity. Convert binary information from n input lines to (maximum of) 2 n output lines. Known as n -to- m -line decoder, or simply n:m or n × m decoder ( m 2 n ). May be used to generate 2 n minterms of n input variables.
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CS2100 MSI Components 6 DECODERS (2/5) Example: If codes 00, 01, 10, 11 are used to identify four light bulbs, we may use a 2-bit decoder. 2x4 Dec 2-bit code X Y F 0 F 1 F 2 F 3 Bulb 0 Bulb 1 Bulb 2 Bulb 3 This is a 2 × 4 decoder which selects an output line based on the 2-bit code supplied. Truth table: X Y F 0 F 1 F 2 F 3 0 0 1 0 0 0 0 1 0 1 0 0 1 0 0 0 1 0 1 1 0 0 0 1
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CS2100 MSI Components 7 DECODERS (3/5) From truth table, circuit for 2 × 4 decoder is: X Y F 0 F 1 F 2 F 3 0 0 1 0 0 0 0 1 0 1 0 0 1 0 0 0 1 0 1 1 0 0 0 1 F 0 = X' Y' F 1 = X' Y F 2 = X Y' F 3 = X Y X Y Note: Each output is a 2-variable minterm ( X' Y' , X' Y , X Y' or X Y )
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CS2100 MSI Components 8 DECODERS (4/5) Design a 3 × 8 decoder . x y z F 0 F 1 F 2 F 3 F 4 F 5 F 6 F 7 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 1 1 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1 0 1 0 0 0 0 0 1 0 0 1 1 0 0 0 0 0 0 0 1 0 1 1 1 0 0 0 0 0 0 0 1 F 1 = x' y' z x z y F 0 = x' y' z' F 2 = x' y z' F 3 = x' y z F 5 = x y' z F 4 = x y' z' F 6 = x y z' F 7 = x y z
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CS2100 MSI Components 9 DECODERS (5/5) In general, for an n -bit code, a decoder could select up to 2 n lines : : : n -bit code n to 2 n decoder up to 2 n output lines
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MSI Components 10 DECODERS: IMPLEMENTING  FUNCTIONS (1/5) A Boolean function, in sum-of-minterms form S decoder to generate the minterms, and an OR gate to form the sum. Any combinational circuit with n inputs and m outputs can be implemented with an n :2 n decoder with m OR gates. Good when circuit has many outputs, and each function
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This note was uploaded on 02/27/2011 for the course CS 2100 taught by Professor Shivakumar during the Spring '11 term at IIT Kanpur.

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cs2100-7-MSI - CS2100Computer Organisation MSI...

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