Digital Design Travis Doom Professor Computer Science Computer

Digital Design Travis Doom Professor Computer Science & Computer Engineering Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

What is Engineering? How does one learn Engineering? Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

What is design? l General model for engineering (Byrne, 1992) Alteration Reverse Engineering Abstraction Conceptual Requirements Design Implementation re-think re-specify Conceptual Requirements re-design re-build Existing System l Forward Engineering Refinement Design Implementation Target System Complex systems have multiple levels of abstraction Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

Logic circuits: Abstraction at work l l l Logic circuits divide into two major types: Combinational Logic – Current output depends on current input only (memoryless!) Sequential Logic – Current output also depends on past inputs (has memory/state) m m m Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

Engineering design: Abstraction at work m m m Cost: 1 m p + m+p Cost: 5 m p * mxp Cost: 10 Design: 2 m m x 2 2 m Any value (including a constant) can be represented Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

Engineering design: Abstraction at work m m m Cost: 1 m p + m+p Cost: 5 m p * mxp Cost: 10 m m + m+m Design: 2 m m 2 m * Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering 2 xm x 2 2 m Doom Digital Systems Design

Engineering design: Abstraction at work m m m Cost: 1 m p + m+p Cost: 5 m p * mxp Cost: 10 m x 2 2 m Cost: 6 m n + x 2 Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering 2 x (m + n) Design: 2 x (m+n) Doom Digital Systems Design

Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

Basic logic circuits l AND gate – Output Z = 1 only when inputs A and B are both 1 – Z = A·B – Z = AB l OR gate – Output Z = 1 only when inputs A or B or both are 1 – Z=A+B l B A B Z Z NOT gate or inverter – Output Z = 1 only when input A is 0 – Z=A – Z = A’ – Z = ¬A l A A Z /A F /B Simple alone, but combine a few million gates and… Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

Integrated Circuits (ICs) l l CLR CLK 16 15 14 13 12 11 10 9 1 2 A 3 B 4 C 5 D 6 ENP 7 GND 8 +5 volts Pin-out view Block diagram view Functional view Analog properties Integration Scale l SSI: Small Scale Integration – 10 s of transistors/unit l MSI: Medium Scale – 100 s of transistors l LSI: Large Scale – 1000 s of transistors l VLSI: Very Large Scale – 100, 000 s+ transistors Pin-out view 74 LS 04 1 2 3 4 5 6 9 8 11 10 13 12 Block diagram Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering 1 K 16 1 9 7 10 3 4 5 6 2 100 KHz 8 VCC RCO QA QB QC QD ENT LD 74 LS 163 VCC CLR LD ENP ENT A B C D QA QB QC QD RCO 14 13 12 11 15 CLK GND Functional view Doom Digital Systems Design

Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

How do we get the electrons to do the work? Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

Logic Gates: An ideal abstraction Schematic Vcc Rc Vin Ra A Z Vout Equation Z = A’ = A GND Active high convention: ON = True = logic “ 1” (current flows) Current Input Vin OFF ON Current Output Vout ON OFF Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Truth Table Current Input Current Output A Z 0 1 1 0 Doom Digital Systems Design

‘Simple’ example non-ideal logic devices Vcc Rb Rb A Ra Ra B B Ra Rc C GND What are the likely intended functions of these devices? Disclaimer: These simplistic implementations are for introductory illustration only. Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

Levels of abstraction in digital computation l The Problem l Algorithm & Language Executing a program requires multiple representations/layers of interpretation (hardware is just another layer) Every level of this hierarchy that you don’t understand is a black box – It might as well be magic – “Debugging by superstition” ISA & Microarchitecture Circuits & Devices Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design

Wright State University, College of Engineering Dr. Doom, Computer Science & Engineering Doom Digital Systems Design