Introduction to Microcomputer Systems

• Outline– What is a Microcomputer?

– Types of Microcomputers

– Modular Microcomputer

– Clock and CPU Control Circuits

– Address Decoder

– Address and Data Bus Buffers

– Buffer Control

– Bus Arbitration Control

– Memory Management

– Memory Module

– Peripherals Module

• Goal– Understand components of modular microcomputer

• Reading– Microprocessor Systems Design, Clements, Ch. 1

What is This Course?

• Learn microcomputer systems– hardware organization

– assembly code and C programming

– hardware interfacing

• Hardware/software combinations– the essence of computer engineering

• Preparation for CPSC 483– build HW/SW projects using same boards

Course Organization

• Lectures– fundamentals of microcomputer systems

– details of Motorola ColdFire single-board computer

» used in labs

• Labs– learn ColdFire hardware

– learn how to program the board in C and assembler

– learn how to control ColdFire resources

– learn how to add and interface hardware peripherals

– learn how to implement applications

References

• Microprocessor Systems Design, 68000 Hardware, Software, and Interfacing, Third Edition, Alan Clements, PWS-KENT, 1997.– text, in bookstore

• Web Site– lecture notes

– lab manual

• Motorola MC68000 Family References– in lab, on Web site

• Motorola ColdFire References– in lab, on Web site

• Chip Data Sheets– in lab, on Web

Grading

• Midterm25%

• Final 25%

• Labs 35%

• HW, Project, Quizzes15%

Topics

• Microcomputer systems

• 68k programmer model

• 68k signal description

• 68k memory hierarchy

• 68k instruction set - briefly

• 68k C and assembly code programming

• Static RAM

• Memory read and write cycles

• Address decoding

• Exceptions - interrupts, exceptions

Topics

• I/O fundamentals

• Parallel I/O & Timers

• Serial I/O

• Microcomputer buses

• Dynamic RAM - organization and timing

• Microcomputer systems design

Assignment

• Read Chapters 1, 2.1-2.3, 7.5, 7.6– Microcomputers

– 68000 programmer model

– Cache memory

– Virtual Memory

– 680X0 architecture - ColdFire is 68060 descendent

• Form lab teams– 2 person teams for lab assignments

» Turn in one lab report, get same grade

– Form teams by first lab

Assignment (cont.)

• If you have PC with CD-ROM drive– get CDROM out of your book

– try to install cross-assembler and C compiler on your PC

– see if they will assemble and compile a simple program

– you can then do coding at home and bring floppy to lab

– note we will use GNU C compiler in class

• Everyone– labs start second week

– read lab assignment in advance

– bring some PC floppies to lab

– end of this week - check that your ID will access HRBB 217

– make sure you have Neo account for class email

What is a Microcomputer?

• Microcomputer (uC) = microprocessor-based computer

• Microprocessor (uP) = single-chip or chipset CPU

• Chipset - few closely-interacting chips– 68020 - integer+control, MMU, floating point

– VAX 8200 - integer+control+MMU, microcode, floating point

• All computers today have single-chip CPU– off-chip delays force all high-speed paths on chip

– 2.26+ GHz P4

» off-chip path is 500 MHz

» 2 levels of memory cache on chip

– “chipset” is interface chip for CPU

» memory interface, mouse, keyboard, graphics, USB, ...

Types of Microcomputers

• Single board computer (SBC)– usually an embedded computer - buried inside a product

• Features– dedicated to a single fixed task

– minimum hardware to support the task

» minimize cost, power, weight, size

• Examples– PostScript printer, ATM, microwave oven, cell phone

• Microcontroller– board shrunk to single chip - most common uC

– CPU, memory, I/O

– Examples: ARM, 68HC11, 8051

Types of Microcomputers

• Modular microcomputer– modules connected by a bus

– usually a general-purpose computer

• Features– used for wide range of applications

– flexible hardware to support application range

» can mix and match modules as needed

» example - add more memory modules

• Examples– personal computer, factory controller

Modular Microcomputer

• System = modules linked by system bus– system bus - data transfer between modules

– local bus - data transfer within module

• Advantages– standard modules assembled to form computer

– large number of module types available

– can easily customize computer to application needs

• System bus standards– bus specification agreed upon by all manufacturers

– often first a proprietary bus

» Motorola Versabus => VME bus

– now industry committees agree to bus standards

Figure 1.1

CPU Module Memory Module Peripherals Module

System Bus

Buffers Buffers Buffers

CPUMMULocal MemoryClockBus Arbitration

DRAMDRAM CtlAddr Decode

Parallel I/OSerial I/OTimerDisk CntlrUSBFirewire...

Clock and CPU Control

• Time reference to CPU.– square or sine wave

– 1000 MHz for 500 MHz Alpha

• Also forms master clock used for rest of system– synchronize bus, other modules

• Power-on reset– force CPU to initialize and execute start-up routine

» bootstrap code

– initiated when power first turned on

» can also initiate manually - the reset button

Address Decoder

• Divide up address space– allocate to individual memory units

• Divide up among memory chips– e.g. split 64 MB across 32 16 Mb DRAM chips

• Partition physical memory locations– local memory on CPU board

» SRAM, EEPROM, Flash, ROM

» data transfer on local bus

» accessible only to CPU

» allows CPU module to be independently tested

– main memory in memory module

» data transfer on system bus

Address and Data Bus Buffers

• uP output pins can only drive small load– a few nearby chips

• Use buffers or bus drivers to drive large buses– chips with big transistors, little logic

– shield uP from load

• Interface between uP and local and system buses

• Need buffer control to coordinate drivers

Buffer Control

• Determines operating mode of bus drivers and receivers– only turn on drivers when they need to send data

– e.g. disable system bus drivers during local memory access

• Only one device can drive the bus at a time– tristate - buffer goes into high impedance state

» like an open circuit

• Operations on parts of a word– e.g. 32-bit uP wants to write one byte or a 16-bit word

– memory has byte addresses

• Byte/word control turns on drivers in part of bus

Bus Arbitration Control

• Master and slave devices– CPU is master

– memory and peripherals are slaves

– CPU controls all bus usage

• Multi-master system– multiple devices can access bus

– DMA (direct memory access) controller

» moves data between memory and peripheral

» autonomous of CPU

– multiprocessor - multiple uPs

• Need protocol (rules) for bus access– one at a time, fair access, timely access

– in hardware for speed

– master - currently controlling bus

– slave - devices accessed by master

Memory Management

• Translate uP logical address to memory physical address– logical address - any address in uP architecture address space

» issued by program

– physical address - actual memory location

• Virtual memory– make small physical memory look like large logical memory

– store part of data on disk

– system vs. user protection domains

• Location independence– programmers use logical address

– operating system figures out what physical address to use

• Memory management unit (MMU)– part of CPU today - 68030, 486, and later

Memory Module

• Types of memory– read/write random access memory (RAM)

– read-only memory (ROM)

» programmed when manufactured

» use for bootstrap programs, fixed code

» example: PostScript interpreter

– EPROM, EEPROM, flash

» program once, or once in a while

» use for program storage, preferences

• Interface– bus interface - buffers, buffer control

– address decoders

– refresh logic

Memory Module (cont.)

• Dynamic RAM (DRAM)– lowest cost/bit - 1 transistor+capacitor per bit

– used for large main memories

– must refresh bits every few milliseconds

• Static RAM (SRAM)– faster

– more expensive - 6 transistors per bit

– often used for cache memory

– often used for battery applications

» holds data at very low power

Peripheral Module

• Interfaces to outside world

• Serial input/output (I/O)– terminal line

• Parallel I/O– printer cable

• Timer– measure time

– generate series of pulses - e.g. interrupt uP at fixed interval

– used for real-time systems

• Disk controller– disk operations

– data format conversion

• Network interface– Ethernet, IEEE 488 bus, etc.

MVME 162

MVME 167

Microcontroller

912B32 - Computer on a Chip

• 0.75 KB byte-erasable EEPROM

• 32 KB flash EEPROM

• 1 KB SRAM

• 8-channel 8-bit A/D converter

• 8-channel 16-bit timer

• 4-channel 8-bit pulse width modulator

• Asynch/synch serial lines

• Interrupt, watchdog, clock timers

• Wait, stop modes

• Hardware breakpoints

• Muxed 16-bit address/data bus

ColdFire MCF5206e