9/15/09 - L14 Functional BlocksCopyright Joanne DeGroat, ECE, OSU1 Combinational Functional Blocks & Rudimentary Logic functions

9/15/09 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU2 Class 14 – Logic Blocks  What is a combinational logic function block  Examples of low level blocks  Material from section 3-5 and 3-6 of text

What is a functional block?  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 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU3

Functional Blocks  Today – Have advanced to Very Large Scale Integrated (VLSI) circuits. Today’s functional blocks  USB controller  Bus controller  ALUs  Register set  PCI controller  ESATA controller 9/15/09 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU4

Typical past blocks  SSI Quad 2 input AND gate Hex inveter Dual D F/F  MSI 4-bit ALU 4-bit Register 9/15/09 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU5

Rudimentary Logic Functions  Value Fixing, Transferring and Inverting  Functions of 1 variable XF=0F=XF=X’F= /15/09 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU6

Implementation of these functions  Implementation of the functions of 1 variable  2 representation for the F=1 and F=0 case 9/15/09 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU7

Extension of this basic function  Was applied to just a single bit  Can be extended to multiple bits  Multibit specification F 3 F 2 F 1 F 0 F(3:0) denotes the same four bits 9/15/09 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU8

Example – Lecture Hall Lighting  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 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU9

Solution  Truth table  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 9/15/09 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU10

Could be bad  There are actually 5 inputs  a 32 entry truth table.  Fig 3-14 from text. Implementation 9/15/09 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU11

And refinement of I’s  Giving a final implementation of 9/15/09 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU12

Enabling  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  Devices controlled Radio Windows 9/15/09 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU13

Formulation  The truth table and implementation  This is a typical enabling circuit. 9/15/09 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU14

Class 14 assignment  Covered sections 3-5 and 3-6  Problems for hand in none  Problems for practice none  Reading for next class: sections 3-7 and /15/09 - L14 Functional Blocks Copyright Joanne DeGroat, ECE, OSU15