ENG3640 Review and Exam Question1 ENG3640 Microcomputer Interfacing Review & Final Exam Structure

ENG3640 Review and Exam Question 1

ENG3640 Microcomputer Interfacing Review & Final Exam Structure


Topics

Programming I/O Interfacing Interfacing Devices Data Acquisition Systems Timing Generation Serial Communication Busses Transmission Lines Memory Interfacing


Course Objectives

Achieves the following goals:1. Learn about Microcontroller architecture2. Understand Software Development 3. Program in assembly language4. Interrupts, DMA, Polling5. Learn Basic I/O techniques (Parallel, Serial)6. Learn Serial communication Systems7. Understand functionality of busses8. Understand Data Acquisition Systems9. Learn about Memory Technology and Interfacing


Q1. Software Development

Problem Statement

DesignStage

EffectiveData Structure

Modular Design

(Procedures)

Implementation

Instruction Set

AddressingModes

AssemblyFormatTesting

Directives


Analysis


Software Development


Program Development


Q2. General Interfacing Switch Debouncing Keyboard Interfacing LCD

+5V

APP7 PP6 PP5 PP4 Selected keys

1110

1101

1011

0111

0,4,8,C,

1,5,9,D,

2,6,A,E,

and 3and 7and Band F

Table 7.6 Sixteen-key keypad row selections

A

B

C

D

E

F

0

1

2

3

4

5

6

7

8

9

10K

VCC

PP7

PP6

PP5

PP4

PP3

PP2

PP1

PP0

68HC12

Figure 7.23 Sixteen-key keypad connected to 68HC12


Hardware Debouncing: Schmitt Trigger

A Schmitt trigger is a special circuit that uses feedback internally to shift the switching threshold depending on whether the input is changing from low to high or high to low.

The difference between V T+ and V T- is called hysteresis. A 74LS14 Schmitt Trigger inverter can be used to debounce a

switch.

VIN

VOUT

2.1 2.9 5.0

V T+

V T-

5.0

Example: 74LS14


Liquid Crystal Displays: Operation

An LCD display requires an alternating excitation wave applied to selected electrodes to change selected areas.

A constant (DC) excitation signal will polarize and destroy the crystal.

60 Hz Oscillator

Control

BP

FP

XOR

VLCD

Front Plane

Liquid Crystal Material

Back Plane


I/O Interfacing


General Interfacing Any MCU would communicate with peripherals through I/O

ports. Types of data

1. Numeric/Alphanumeric2. Control/Status Information

Basic I/O Transfer alternatives can be classified as 1. MCU Initiated2. I/O Device Initiated

MCU Initiated Device Initiated

UnconditionalTransfer

Polling(Gadfly)

InterruptsDirect Memory

Access

Periodic Polling


Synchronization Techniques


Q3. Timer Module

Input Capture: “captures the time at which an external event occurs”. Can be used to:

1. Generate interrupts and

2. Measure period or pulse width Output Compare: “can generate a periodic

pulse with a programmable polarity, duration, and frequency”. Can be used to:

1. Create periodic interrupts,

2. Generate: Pulses, Square waves

3. Measure frequency


General Understanding of TIM


Q4. DAQ

Real

World

Measurand

Transducer

(sensors)

Analog

Mux

Signal

Conditioning

Sample and

Hold Circuit

A/D

ConvMCUD/A

ConvActuator


Analysis or Design of Signal Conditioning


Data Acquisition Systems


Q5. DACs or ADCs

A/D converters are classified according to several characteristics

Resolution (number of bits) typically 8 bits to 24 bits Speed (number of samples per second) – several

samples/sec to several billion samples/sec Accuracy – how much error there is in the conversion

Classification1. Staircase ADC2. Tracking ADC3. Successive Approximation Converters4. Flash A/D Converters5. Integrating A/D Converters


Important Circuits in DAS


Q6. Serial and Parallel Communications

Transmitter Receiver

CLK


Understanding of the Technology


Serial Communication Systems


Bus Protocols

Protocol refers to the set of rules agreed upon by both the bus master and bus slave Synchronous bus transfers occur in relation to successive edges

of a clock Asynchronous bus transfers bear no particular timing relationship Semi synchronous bus Operations/control initiate asynchronously,

but data transfer occurs synchronously

CPU Device 1 Device 2 Device 3

Bus

ENG3640 Review and Exam Question

25ENG3640 Fall 2009 25

Transmission Line Models

When can the R and G terms be ignored in the ZWhen can the R and G terms be ignored in the Z00?? As ww increases, the impact of R and G decreases. When the frequency increases above 100 kHz, the terms

multiplied by ww start to dominate.


Reflections on the Bus To reduce reflections, the ends of a transmission line

should be terminated by connecting a resistor equal to Z0 across the line

Connecting a resistor between the bus and VCC will pullup the lower logic level and reduce noise immunity

Classic Solution: connect two resistors to the bus one to the ground and one to VCC R1//R2 = Z0

RT

VT

RT = R1//R2 = Z0

Bus


Lattice Diagram Analysis – Key Concepts

Diagram shows the boundaries (x =0 and x=l) and the reflection coefficients

Time (in T) axis shown vertically

Calculate voltage amplitude for each successive reflected wave

Total voltage at any point is the sum of all the waves that have reached that point

Vs

Rs

ZoV(source) V(load)

TD = N ps0

Vs

RtThe lattice diagram is a tool/technique to simplify the accounting of reflections and waveforms

Time V(source) V(load)

a

source load

bA

cA’

B’

dB

e

0

N ps

2N ps

3N ps

4N ps

5N ps

ENG3640 Review and Exam Question 28ENG3640 Fall 2009 28

What Should Designer do? Practically there are several ways to mitigate the negative

impact of reflections:1. Wait long enough after each signal transition for the reflection on

the line to die out (OK for low speed but not high speed systems)

2. Decrease the frequency of the system so that reflections reach steady state before another signal is driven onto the line (Low Speed Sys!)

3. Shorten the Bus or (PCB trace) so that reflections will reach steady state in a shorter time (not practical or sometimes impossible!)

4. Terminate the transmission line with an impedance equal to the characteristic impedance of the line:

Use a matched termination at far end. Thereby producing no reflections on the line

Use a matched termination at source end absorbing the wave reflected from the far end.


Why, How to solve Reflections


Q7. Memory


Understanding the Principle of Operation


Address Decoding



Documents

ENG3640 Review and Exam Question1 ENG3640 Microcomputer Interfacing Review & Final Exam Structure