Combinational Functional Blocks Rudimentary Logic functions 9 15 09

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Class 14 – Logic Blocks o What is a combinational logic function block Examples of low level blocks o Material from section 3 -5 and 3 -6 of text o 9/15/09 - L 14 Functional Blocks Copyright 2009 - Joanne De. Groat, ECE, OSU 2

What is a functional block? o o In the design of digital circuits certain operations are present in many designs. The specific logic circuits for that function can be formed into a functional block that can be reused many times. In the past (ancient times ) many of these were manufactured on integrated circuits, small-scale(SSI) and medium-scale(MSI). 9/15/09 - L 14 Functional Blocks Copyright 2009 - Joanne De. Groat, ECE, OSU 3

Functional Blocks o Today – Have advanced to Very Large Scale Integrated (VLSI) circuits. n Today’s functional blocks o o o 9/15/09 - L 14 Functional Blocks USB controller Bus controller ALUs Register set PCI controller ESATA controller Copyright 2009 - Joanne De. Groat, ECE, OSU 4

Typical past blocks o SSI n n n o Quad 2 input AND gate

Rudimentary Logic Functions o Value Fixing, Transferring and Inverting o Functions of 1 variable n n n X 0 1 9/15/09 - L 14 Functional Blocks F=0 F=X’ F=1 0 0 1 1 0 1 Copyright 2009 - Joanne De. Groat, ECE, OSU 6

Implementation of these functions o o Implementation of the functions of 1 variable 2 representation for the F=1 and F=0 case 9/15/09 - L 14 Functional Blocks Copyright 2009 - Joanne De. Groat, ECE, OSU 7

Extension of this basic function o o o Was applied to just a single bit Can be extended to multiple bits Multibit specification n n F 3 F 2 F 1 F 0 F(3: 0) denotes the same four bits 9/15/09 - L 14 Functional Blocks Copyright 2009 - Joanne De. Groat, ECE, OSU 8

Example – Lecture Hall Lighting o o The problem: 3 modes of operation for two switches, one on podium and one on wall. Mode M 0: Either switch P or R turn house lights on or off. Mode M 1: Only switch P turns house lights on or off. Mode M 0: Only switch R turns house lights on or off. 9/15/09 - L 14 Functional Blocks Copyright 2009 - Joanne De. Groat, ECE, OSU 9

Solution o Truth table o Input P=0 says lights off, 1 says lights on Input R=0 says lights off, 1 says light on Mode says who has control o o 9/15/09 - L 14 Functional Blocks Copyright 2009 - Joanne De. Groat, ECE, OSU 10

Could be bad o o There actually 5 inputs a 32 entry truth table.

And refinement of I’s o Giving a final implementation of 9/15/09 - L 14

Enabling o Problem: Some devices on your car only work if key is in the ignition and turned on. Ignition Switch – IG 0 if off and 1 if on o Devices controlled o n n Radio Windows 9/15/09 - L 14 Functional Blocks Copyright 2009 - Joanne De. Groat, ECE, OSU 13

Formulation o The truth table o This is a typical enabling circuit. 9/15/09 -

Class 14 assignment o o Covered sections 3 -5 and 3 -6 Problems for hand in n o Problems for practice n o none Reading for next class: sections 3 -7 and 3 -10 9/15/09 - L 14 Functional Blocks Copyright 2009 - Joanne De. Groat, ECE, OSU 15

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