The Microcontroller
Common
component in modern electronic systems
Single-chip computer
Microprocessor-based device
Completely self-contained with memory
and I/O
Primary
role: provide inexpensive, programmable logic control and interfacing to
external devices
e.g., turn
devices on/off, monitor external conditions
Microcontrollers used in a wide number of electronic systems such as:
·Engine management systems in automobiles
·Keyboard of a PC
·Electronic measurement instruments (e.g., digital multimeters, frequency synthesisers, and oscilloscopes)
·Printers
·Motor controls
·Security systems
·Cordless and cellular phones
·Televisions, radios, CD players, tape recording equipment
·Hearing aids
·Security alarm systems, fire alarm systems, and building services systems
·Microwave ovens
·Handheld tools
·Remote control devices
·Many, many more
What is a microprocessor?
A
device that integrates a number of useful functions into a single IC package
Some functions are:
·Ability to execute a stored set of instructions to carry out user defined tasks.
·Ability to access external memory chips to read/write data from/to memory.
·Ability to interface with I/O devices
 |
|
These
form the basic connections between the microprocessor and its memory devices.
|
What is I/O?
I/O is Input/Output. It can be:
·A
number of digital bits formed into a number of digital inputs or outputs
called a port
usually eight bits
wide
referred to as
a BYTE wide port
·A
serial line from/to the microprocessor
(Transmit or TX) and a
serial line to the microprocessor (Receive or RX)
Allows serial data (bit
stream) to be transmitted/received via a two-wire interface
·Other
I/O devices
Analog to Digital
Converters (ADC) and Digital to Analog Converters (DAC)
Timer modules
Interrupt controllers
Relatively
complex subsystems
Can be obtained as separate ICs (e.g.,
Intel 8255 PPI, 8259 PIC, 8254 PIT)
Connected to microprocessor in a similar manner to that of the memory devices
Often contain their own memory to support internal operations (ie. registers).
What is a microcontroller?
Basically, a device which integrates a number of the components of a microprocessor system onto a single chip
Only need to be supplied power and clocking
Microcontroller combines on the same chip:
·The CPU core
·I/O
·Memory
PROM/EPROM/EEPROM/Flash memory
Variable RAM memory
Most microcontrollers will also combine other devices such as:
·A Timer module to allow the microcontroller to perform tasks for certain time periods.
·Serial I/O (UART) for data flow between microcontroller and devices such as a PC or other microcontroller.
·Analog input and output (e.g., to receive data from sensors or control motors)
·Interrupt capability (from a variety of sources)
·Bus/external memory interfaces (for RAM or ROM)
·Built-in monitor/debugger program
·Support for external peripherals (e.g., I/O and bus extenders)
A typical microcontroller; the different sub units integrated onto the microcontroller chip.
The
heart of the microcontroller is the CPU core
Traditionally
based on an 8-bit microprocessor unit
e.g., Motorola
uses basic 6800 microprocessor core in M68HC11 microcontroller devices
Some
differences between microprocessors and microcontrollers
MP:
suited to contro of I/O devices requiring a minimum component count
MC: suited to processing information
in computer systems
Instruction
sets:
MP: processing
intensive
powerful addressing modes
instructions to perform complex operations & manipulate large volumes
of data
processing capability of MCs never approaches those of MPs
large instructions -- e.g., 80X86 7-byte long instructions
MC: cater to control
of inputs and outputs
instructions to set/clear bits
boolean operations (AND, OR, XOR, NOT, jump if a bit is set/cleared), etc.
Extremely compact instructions, many implemented in one byte
(Control program must often fit in the small, on-chip ROM)
Hardware
& Instructionset support:
MC: built-in I/O operations, event timing, enabling & setting up priority
levels
for interrupts caused by external stimuli
MP: usually require external circuitry to do similar things (e.g, 8255
PPI, 8254 PIT,
8259 PIC)
Bus
widths:
MP: very
wide
large memory address spaces (>4 Gbytes)
lots of data (Data bus: 32, 64, 128 bits wide)
MC: narrow
relatively small memory address spaces (typically kBytes)
less data (Data bus typically 4, 8, 16 bits wide)
Clock
rates:
MP very fast
(> 1 GHz)
MC: Relatively
slow (typically 10-20 MHz)
since most I/O devices being controlled are relatively slow
Cost:
MP's expensive
(often > $100)
MCs cheap
(often $1 - $10)
4-bit:
< $1.00
8-bit:
$1.00 - $8.00
16-32-bit: $6.00
- $20.00
Microcontroller
Software and Programming Tools
Programming
Generally
done in either the core's native assembly language or C
Sometimes
HLL support (often BASIC) is available
Assemblers/Linkers
often supplied free by the micro's manufacturer
C compilers
vary from free and very buggy to very expensive and only moderately buggy
Environments
generally not friendly or reliable
Downloading
Program development
usually done on a PC
Software
tools must produce a file to download to the MC's EPROM
Several standard
formats (e.g., binary, hex)
EPROM burner
often necessary
Can download program to an EPROM emulator
But to reprogram, must us an UV
erasor first
Flash memory
programmers make this easier
Very easy to reprogram
with inexpensive "in-circuit debugger"
Interacts with MC via 3 pins + power + ground
Or can be programmed/debugged with a resident monitor program
on-chip UART for communications with PC
No burner or UV erasor
needed
No expensive quartz
window required
Expedites program-test-erase-reprogram
code development cycle
Monitor
A program
module that communicates with PC software
Typically
uses a serial port to talk to a PC's terminal program
Capabilities
vary widely
Usually can
send/receive text and ASCII-converted numbers
Often has
commands to examine/change registers, memory locations, I/O ports
All memory space on same bus
Every location has unique address
So instructions and data treated the same way
Possible bottleneck between instruction and data fetches
Overcome with instruction prefetching (overlapping, pipelining) and/or Instruction/Data
caches
Simplifies processor design -- one memory interface
More reliable -- fewer things can fail
Also RAM can be used for both data and instruction storage
Greater flexibility in design of software (esp. real-time OS)
PC (80X86/Pentium) uses this arquitecture
(except for separate I/O address space)
Motorola 68HC11 microcontroller
Harvard
Architecture
Code and
data strorage areas (address spaces) on separate buses
Potentially
more efficient
Instructions execute in fewer cycles
Since greater instruction parallelism possible
Instructions and data fetched simultaneously
(new instruction fetches can occur during prior instruction execution)
Example: Microchip's
PIC microcontroller
Princeton
won early competition
Better suited
to technology of the time
CISC vs.
RISC
CISC
(Complex Instruction Set Computers)
Tend to have
many instruction in instruction set
Can carry
out complex operations
(many used very infrequently)
Many are
very long (many bits)
And require
many clock cycles
RISC
(Reduced Instruction Set Computer)
Few instructions
Simple instructions
Short (few
bits) and fast
Often orthogonal
instruction sets
Can read/write/use all registers in same way
Allows for great power and flexibility
Example PICmicro
Many other
microcontrollers use RISC
Some microprocessors offer both CISC and RISC features
Microcoded versus Hardwired
processors
The under cover design of a processor
Microcoded
Processor
within a processor
Signals required
to execute instructions "fetched" from internal "Control ROM" memory
Allows for
great flexibility in instruction set
Easier to
design
Slower than
hardwired
Hardwired
Signals required
to execute instruction generated by logic gates (combinational circuitry)
The "control matrix"
Faster
Less flexible
Microchip's PICmicro
Motorola 68HC11
Hitachi H8 (used in the
LEGOS RIS RCX)
Intel 8051
Introduced
in late 70s
At the heart of the biggest variety
of micros on earth
Biggest player now Philips Electronics
(Intel concentrating on PC CPU chipset)
General pros:
Powerful bit manipulation instructions
part of RAM and many special registers are bit-addressable.
Multiply
and divide instructions.
At least
two 16-bit timers.
UART capable
of 500kb/s at 16MHz on all but very small parts.
Plentiful
internal RAM.
Straightforward
code addressing - always starts at zero.
I/O design
makes bi-directional I/O easy.
Excellent
free assembler from Metalink
Free C compiler
available
General cons:
Very quirky instruction set
Confusing
variety of internal and external memory spaces.
I/O design
prevents true floating inputs, and pins are always high after reset.
Not very
fast due to clock division.
Access to
external data very weak - single pointer register only.
Poor compiler
support - no stack-relative access.
Watchdog
not standard
Microchip's PICmicro
Modern
PIC16F452 trainer used in first half of this course
RISC
Harvard Architecture
Some pros:
Simple
instruction set
Robust hardware
Excellent support
Microchip's MPLAB free development
environment
Wide range of sizes and peripheral
choices
Many language and tool choices
Some cons:
4 times slower at same clock speed
Relatively weak instruction set
Limited code and data addressing
Complex "banked" addressing
Accumulator-based data processing
Single "working" acculumulator
Motorola 68HC11
Some pros:
Competetive
with 8051
Von Neumann architecture is easy to
understand
Powerful, easy-to-use instruction
set
Popular parts are good value
Good support for C compilers
Good support from Motorola
Some cons:
Weak
timers
No consistency within family - many
variants specialised
Evaluation board (EVB) is expensive,
unreliable
Not price-competitive
Slow
Old technology
Hitachi H8
Used
in LEGO Mindstorms Robotics Invention System RCX
Similar architecture to the HC11
Some pros:
Many
devices with flash.
Powerful instruction set with good
C support
Wide range of 8 and 16-bit devices
Good free C compiler
Nice evaluation/programming boards
available
Abundant timers and interrupts
Some Cons:
Most
packages surface-mount
Emulation
expensive