micro lecture 3

8/3/2019 Micro Lecture 3

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Microprocessor Systems I 1

Programming the Z80 MPU

To create a program that will execute on theZ80 MPU, we need to know several things.

1. The Programming Model which includes

The Instruction Set , Register Set and theAddressing Modes .

2. The System Memory Map :- This gives

information regarding the address locationsand sizes of the Memory (RAM & ROM) and

the I/O devices


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ROM: contains

program, constants,lookup tables

RAM: contains

variables and

data structures

I/O : Input Output

device/s location/s


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3. The Development Tools to allow the creation of

a machine readable program

4. Finally, the problem , a description program that

we want to implement.

Once we have an idea of what we are trying achieve,

then we can design a program to this.

(MicroBook Page 100)


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In the previous lectures we have introduced the

basic concepts of how a general MPU operates.

These next lectures will specifically with the

Z80 MPU.

The lectures will introduce the following

1. INSTRUCTION SET and ADDRESSING MODES

2. INTRODUCTION TO ASSEMBLY LANGUAGE


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Refresher

MPU instructions are represented by binarywords.

Each instruction has an unique binary

pattern.

MPU executes program one instruction

at a time. ( FETCH DECODE EXECUTE )


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MPU Instruction Set:

The MPU is only capable of performing a limitednumber

of instructions , this is its instruction set.

Zilog Z80 MPU can execute 158 different instructions

types.

The types of instructions a MPU can perform may be

generally classified as follows


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LD A, ( 1825H)Assembler

Format

Operator

Opcode

Operand(s)

Instruction

Hex Code : 3A

Process

to carry out

Data to usein the process

1825


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1. Data Transfer Operations2. Arithmetic Operations

3. Logical Operations

4. Program Flow Control5. Input - Output

6. Miscellaneous


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Data Transfer

LD A, 5 transfer constant data 5 into Accumulator

LD HL, 1900 HL loaded with 1900H

Arithmetic Operations

ADD A,5 add constant 5 to Accumulator

SUB 5 subtract 5 from the Accumulator


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Logical Operations

OR 0FH bitwise OR of Acc with constant 0FH

AND 0FH bitwise AND of Acc with constant 0FH

Program Flow Control

JP Z,0200H

JP NZ,0200H

JP C,0200H

JP NC,0200H

DJNZ 0200H ;THIS OPCODE USES REGISTER B


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Z80 Instruction Set Uses the following

Categories to group its operations

Load and Exchange

Block Transfer and Search

Arithmetic and Logical

Rotate and Shift

Bit Manipulation (Set, Reset, Test) Jump, Call, and Return

Input/Output

Basic CPU Control


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Addressing Modes

Most Z80 Instructions operate on Data stored in

1. Internal Registers ( A,F,B,C,D,E,H,L,SP, e.t.c.)

2. External Memory

3. In I/O Ports

For all these Data movement operations, the instruction

( the op-code + operands) must contain information

relating to

1. Source of Data (Is it Register,Memory or I/O ?)2. Destination of Data (Register,Memory or I/O ?)


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Instructing the MPU as to the Data source and the Data

Destination is called the ADDRESSING MODE.

MPU generally have a variety of ADDRESSING modes

The Z80 supports 10.

The Instruction Format is as follows

SPECIFIES

OPERATION

SPECIFIES

DATA VALUESOR

ADDRESS OF

DATA


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The Z80 Instruction Set Contains Operations

described with the following 3 instruction formats

1. Single Byte Op-code Only

2. Two Bytes Op-code + 1 Operand3. Three Bytes Op-code + 2 Operands


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Reading Mnemonic

16 Bit Load Operation

LD HL , DE

SRCDEST

DEST = DESTINATION (Reg, Mem , I/O )

SRC = SOURCE (Reg , Mem , I/O )

OPCODE OPERAND1 OPERAND2


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Z80 Addressing Modes

Ref. Microprocessor Systems Chapter 3 Pg. 63 - 69

1. Register Addressing (Implied, Implicit)

Instruction execution involves only contents of

registers for source and destination.

No memory address need be generated

LD A,B

LD BC,DE SINGLE BYTE INSTRUCTION

ADD A,C FORMAT

Special Case OR 45 means OR ACC with 45


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2. Immediate Addressing

In this mode the data required by the instruction is

available immediately the full instruction has beenread.

2 BYTE and 3 BYTE INSTRUCTION FORMAT

OPCODE followed by DATA Byte(s). Data is oftencalled LITERAL,(meaning a quantity itself)

LD B,34H 2 BYTE FORMAT OPCODE + OPERAND

ADD A,0EAH

LD BC,1850H 3 BYTE FORMAT OPCODE+OPR1+OPR2

OR 02H


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3. Direct Addressing

(Also called Absolute)

This mode the instruction OP-CODE is followed by a

2 byte (16 bit) Address.

The Address is the exact address of the data item. TheAddress is a constant since it is contained within the

program

LD (1234),A

IN A,(FA)


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4.Indirect Addressing

In this case the instruction does not give the address

directly but instead the location of the address.

This location may be another memory location ora register.

If the location is in memory the addressing mode is

called Memory Indirect.

If the location is in a register it is called Register

Indirect.

LD (HL),A ADD A,(DE)


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5. Index Addressing

Using Index Register + an Offset to Specify data

Index registers IX and IY (16 bit registers)

LD A,(IX + 0) ; address formed from IX contents + 0h

6. Relative Addressing

In this mode , the byte following the instruction

op-code specifies a 2s complement displacement

value. The 2s complement value is added to the

PC to enable forwards and backwards jumps in theprogram.


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1850 JR NZ,0FBH

1852 RST 38H

0FBH means 1111 10110000 0100 1s complement

0000 0101 2s complement

5 DECIMAL

FB = -5 DECIMAL

IF when executing the jr instruction the Z is still set

the PC counter will be altered to jump back five

places to location 184DH

NB. The PC will be pointing the next instruction location

1852H , therefore 1852H - 5H = 184DH


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Why do we need different Addressing Modes ?

Read Discussion on Page 70.

Register AddressingReduces external Bus access.


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Introducing Assembly Language Programming

The section deals with the creation of programs

that will execute on the Z80.

The programs will initially be hand assembled.

These result hex numbers , representing the program

will be entered, by hand into MPU memory system.

Later development tools such as a PC based

Z80 cross-assembler and Z80 simulator will be used

to develop and debug larger programs.

The following pages show a typical Z80 program

with its Listing and Hex Files.


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org $0

jp start

org $1800

start ld hl,$1850

ld b,$20

xor aloop ld (hl),a

inc hl

dec b

jr nz,looprst $38

end


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AS80 Assembler for i8080 [1.31].

Page 1

--------------------------------- FIRST.ASM ------------------

----------------

12 lines read, no errors in pass 1.

0000 = org $0

0000 : c30018 jp start

1800 = org $1800

1800 : 215018 start ld hl,$18501803 : 0620 ld b,$20

1805 : af xor a

1806 : 77 loop ld (hl),a

1807 : 23 inc hl

1808 : 05 dec b

1809 : 20fb jr nz,loop

180b : ff rst $38

No errors in pass 2.


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:03000000C3001822

:0C1800002150180620AF77230520FBFFC5

:00000001FF

micro lecture 3

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