68000 68000 MicroprocessorMicroprocessor

The 68000 Microprocessor

CPU

Memory Output Input

Address bus

Data bus

Control bus

System Bus

i. Address bus: single direction (1 way) bus

transfer the address data

code to memory or devices

ii. Data bus: bidirectional (2 ways) bus

transfer data to/ from the CPU

iii. Control bus: Control all the activities of the

elements

Central Processing Unit (CPU)

o HEART of the systemo Master CONTROLLER for all operationso 3 main parts:

i. ALU : mathematic operation (plus, minus,

multiply, divide, etc.)

ii. Register : storage unit

iii. Control and Timing : Control unit

Memory

CPU DeviceRead Write

(Send data)(Accept data)Device

Semiconductor Magnetic Optical

RAM ROM Disk Tape CD-ROM

StaticRAM

DynamicRAM

Mask-programmable ROM

Programmable ROM (PROM)

Erasable PROM (EPROM)

Electrically EPROM(EEPROM)

MEMORY

Memory cont…

RAM (Random Access Memory)

ROM (Read Only Memory)

• Volatile • Read & Write• Store temporary data

• Non-volatile• Read• To get started from power

on (boot up), including BIOS (basic input/output system)

Input / Output

Programmer’s Model of 68000

Status Register

Functional Description of the 68000

Interrupt control

6800 peripheral

control

System control

Bus arbitration

control

Asynchronousbus control

Processor status

ADDRESS

68000 Data Organization

Byte View1 byte

(8 bits)

000000

000001

000002

000003

.

.

FFFFFF

68000 Data Organization cont…

Word View

68000 Data Organization cont…

Long Word View

Memory Map of 512KB Macintosh

68000 Instruction Types

8-bit : ADD.B D4, D5

D4 11

+ D5 12

D5 23

68000 Instruction Types cont…

16-bit : ADD.W D4, D5

D4 11 22

+ D5 33 44

D5 44 66

68000 Instruction Types cont…

32-bit : ADD.L D4, D5

D4 11 22 33 44

+ D5 22 33 44 55

D5 33 55 77 99

Advantages of MC6800

It is popular to use because it is still using for Macintosh computer.

Instructions set are comprehensive. Compare with the 8-bit P (like 6800, Z-80),

the space for the address is big. There is special characteristic for designing

the operation system. Easy to use by user compiler and assembler

language.

Tutorial

2.1 16 bits

2.2 49,152 bytes

2.3 To store the programs and data

2.4 Volatile and non-volatile

2.5 A bus is a wire or wires that connect the IC chips in a computer

2.6 Unidirectional

2.7 Bidirectional

Tutorial

2.8 ALU, register, timing and control2.9 Each user gets 32KB of RAM. The

operating system does indeed required some RAM for its own use. One way to do this is to allocate a small portion of each user’s RAM for operating system functions.

2.10 The .B, .W and .L extensions specify the operand size for an instruction.

2.11 Longword at address 30 is 9AFC3007. Word at address 30 is 9AFC.

Tutorial

2.12 a. longword

b. longword

c. longword

d. word or longword

e. byte, word or longword2.13 The condition codes are contained in the user byte

of the status register

2.14 Trace bit, supervisor state and interrupt mask are contained in the system byte of the status register.