introduction to programming - welcome to matc

Introduction to Programming

Chapter 2Microcontrollers

Copyright 2005 Richard Lokken

Objectives

Describe the difference between source code and machine code.

Define opcode, operand, and address of an operand.add ess o a ope a d

Explain the purpose of memory addressing modesaddressing modes


Objectives

Show how memory addressing modes work in the HC11

Explain how an instruction is fetched from memory and executed by the o e o y a d e ecuted by t eprocessor.

Use flowcharts to show the Use flowcharts to show the flow/function of a program.


Programming the Computer

Types of Computers Dedicated computersp

• designed to run only one program • computers in your car – microcontroller

General-purpose computers• designed to run multiple programs

• desktop computer running• desktop computer running• word processor• spreadsheet, etc.


Levels of Program Languages

Lowest Level Machine Code

Highest Level Highest Level Basic


Source Code

Written in a programming language English like words that communicate g

instructions to the computer.

Levels of programming languagesp g g g g


Relative Level of Programming

Highest LowestHighestLevel

LowestLevel

BASIC MachineCode

AssemblerC


Programming Levels

English

if X is equal to Y, thent Z l t X

BASICif (X==Y) then Z=X

Cif (x==Y)

set Z equal to X,otherwise set Z equalto Y

elseZ=Yend if

( )Z=X;elseZ=Y;

AssemblerLDAA XCMPA Y

MACHINE96 0091 01CMPA Y

BEQ PASTLDAA Y

PAST STAA Y

91 0127 0296 0197 02


Advantage of High-Level

Source code is portable

Must be compiled


Assembler Language

Close to actual machine code

Portability limited to processors within the same familywithin the same family.

Ad i d b ll Advantage is tends to be smaller and run faster


Machine Code

Only language that computer hardware understands

Referred to as object code In binary Consists of

operational codesp operands (data) address of the operands


OPCODES

Multi-bit code that identifies the instruction

Contains information about the instruction and how to execute the st uct o a d o to e ecute t einstruction

Single instruction will be Single instruction will be implemented with one or more opcodes


opcodes

Operand

Data that is required by the instruction addition instruction adds operands load instruction reads an operand from p

an address and loads it into a processor register.

Operand field is a group of up to three bytes following the opcode.


g

Address

Pointer into memory.

Each memory address is an unique address by which it is identifiedaddress by which it is identified.

Add i b f Address points to a byte of memory


Address Types

Absolute A complete address or an address that p

contains all the address bits

Offset commonly used to allow addressing of commonly used to allow addressing of

memory without specific reference to the entire address.


HC11 Machine Code

Made up of OPCODES, operands, and addresses.

Uses an 8-bit OPCODE and supports various ways of accessing operands i in memory.

256 unique OPCODES can be t dgenerated.

WHY?


Prefix for Number Representationbinary %

octal @

decimal nothing or &

hexadecimal $


Immediate ModeMachine Code Source Code

86 10 LDAA #$10

opcode immediate data

mnemonic


Extend ModeMachine Code Source Code

B7 01 9B STAA $019B

extended modeeffective address


effective address

Inherent ModeMachine Code Source Code

1B ABA


Memory Addressing Modes Immediate

operand immediately follows the opcode in memorymemory

Absolute used to access operand directly from memory

Implied location of the date implied by the instruction


Memory Addressing Modes

Indexed uses an address in an index register g

combined with an address offset

Relative used to change the flow of the program used to change the flow of the program


HC11 Addressing Modes

Immediate (IMM) LDAA #$29$

# indicates IMM mode


Extended (EXT)

Motorola’s name for Absolute Addressing

LDAA $000B LDAA $000B


Direct (DIR)

A form of absolute addressing

LDAA $0B

8-bit address becomes the low-order b f h ff i ddbyte of the effective address.


Inherent (INN)

Used when the operand is inherent or implied. The operands are already contained in the processor registers.

ABA ABA INX


Indexed (INDX, INDY)

used when the operand may be at varying addresses with the 64k

memory map.

LDAA $02,X $02 is an offset X is used for the effective address

calculation


Relative (REL)

Used only for branch instructions. relative mode instructions do not relative mode instructions do not

process data, but control the flow of the program.t e p og a


Processing Instructions

Machine cycles a short set of steps that are performed p p

during a single clock cycle. HC11 performs a four step process

during each machine cycle.


Four Step Process

Phase One Controls steps one and twop Deal with the program counter

Phase Two Phase Two Controls the last two steps Deals with memory access and Deals with memory access and

processing


Fetch Cycle

reads the instruction OPCODE from the memory.

instruction OPCODE is always located in memory at the address ocated e o y at t e add essthat is contained in the program counter.ou

first machine cycle for each instruction


instruction.

Machine cycles

1. Move contents of the PC to the MAR2. Increment the PC. MAR to address 2. Increment the PC. MAR to address

bus3 Enable memory OPCODE put on 3. Enable memory OPCODE put on

data bus4 OPCODE to the IR where it is 4. OPCODE to the IR where it is

decoded.


Execute Cycle

requires one or more machine cycles built-in sequence of events that built in sequence of events that

completes the operation of the instruction.st uct o

instruction execution is unique for each instructioneach instruction


Example

LDAA #$A8 Fetch – 1 machine cycley Execute – 1 machine cycle

1 PC to MAR1. PC to MAR2. Increment PC

E bl l ti d 3. Enable memory location, operand put on data bus


4. Operand loaded in AccA

LDAB $019B Fetch – 1 machine cycley Execute – 3 machine cycles


Example

ABA Fetch – 1 machine cycley Execute – 1 machine cycle

STAA $20Fetch 1 machine cycle Fetch – 1 machine cycle

Execute – 2 machine cycles


Program Flow

First document what the program is going to do.

Defects, undesirable behavior, BUGS


Flowcharting

A means of organizing the flow of a program.


SymbolsTerminator used to show start used to show a subroutineTerminator used o s o s a

or end of program

Pused to show a

subroutine process

Process processshows flowchart continues on samepage

input/output used to show anydata input/outputoperations

shows flowchart continues toanother page

used to show processd i i

direction of flow


decision decisions

introduction to programming - welcome to matc

Documents