218L11S09 - 3/10/09 ESE218 Spring 2009 Lecture 11 1 ESE218...

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Unformatted text preview: 3/10/09 ESE218 Spring 2009 Lecture 11 1 ESE218 Lecture 11: Decoders and encoders Outline Applications in digital systems Binary decoders 2x4 binary decoders active-high outputs, minterms active-low outputs, Maxterms Enable inputs and extension Inverter as a decoder Implementation of binary functions using decoders Encoders with priority Summary 3/10/09 ESE218 Spring 2009 Lecture 11 2 von Neumann architecture John Louis von Neumann (1903-1957) "The Principles of Large-Scale Computing Machines, 1946 Promotion of the stored program concept Both data and Instructions stored in the same memory 3/10/09 ESE218 Spring 2009 Lecture 11 3 A 2-bit row code: MSB = LSB = Address decoder N inputs 2 N outputs: 1 1 Binary Decoder Only one output is active at a time! Decoded row Addressing memory cells in RAM with binary decoders The task can be solved with an array of AND gates. Each of the AND gates decodes a particular input combination. 00 01 10 11 3/10/09 ESE218 Spring 2009 Lecture 11 4 Decoding with one level circuit: multi-input gates needed 3 2 1 m# 1 Y 3 1 Y 2 1 Y 1 1 1 X 1 1 Y 1 1 X X X 1 Y 1 = X X 1 Y 0 = X X 1 Y 2 = X X 1 Y 3 = X X 1 Binary inputs In this decoder always one output is hot. The decoder is always ENABLED Decoders with active-high outputs are minterm generators Y 3 1 2 3 4 5 6 9 10 8 12 13 11 Y 2 Y 1 Y = m 3 = m 2 = m 1 = m This decoder is built with 2-input AND gates and inverters 3/10/09 ESE218 Spring 2009 Lecture 11 5 Decoders with active-low outputs 3 2 1 M# 1 1 1 Y 3 1 1 1 Y 2 1 1 1 Y 1 1 1 X 1 1 1 1 Y 1 1 X X Y 3 1 2 3 4 5 6 9 10 8 12 13 11 X 1 Y 2 Y 1 Y Y 1 = X + X 1 Y = X + X 1 Y 2 = X + X 1 Y 3 = X + X 1 Binary inputs One output is 0 at a time = M 3 = M 2 = M 1 = M generate Maxterms A single output is at a low logic level, all the rest are at a high logic level 3/10/09 ESE218 Spring 2009 Lecture 11 6 Implementation of switching functions 1 2 3 4 5 6 9 10 8 12 13 11 X Y 3 X 1 Y 2 Y 1 Y Binary inputs ..with a Decoder.....
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This note was uploaded on 04/12/2009 for the course ESE 218 taught by Professor Donetsky during the Spring '08 term at SUNY Stony Brook.

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218L11S09 - 3/10/09 ESE218 Spring 2009 Lecture 11 1 ESE218...

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