• A2:
• AQA Microncontroller
• Arithmetic, Logic
• Count to 99
• Bit Masks
• IO Ports
• Microncontrollers
• Tristate Logic
• reviseOmatic
• Polling/Interrupts
• Port Writing
• Subroutines
• Run the Simulator
•  

A2

System on a Chip

A family of integrated circuits that contain all the sub-systems needed to make programmable control systems on a single chip.

Compare this with a traditional PC where multiple chips and subsystems are needed. Smart-phones and tablet PCs use many techniques "borrowed" from microcontrollers and are working towards one-chip designs.

• Processor
• Data bus, instruction bus, address bus and control bus
• Memory
  • Flash to hold the program
  • RAM to hold temporary data
  • ROM to hold permanent code such as the serial communications chip programming routines.
• Input port/s
• Output port/s
• A serial link to allow the chip to be programmed
• Many chips have extra built-in features like
  • analogue inputs with an ADC
  • pulse width modulation outputs for motor speed control
  • serial output for connecting to LCD text displays

Von Neumann Architecture

Processors based on the Von Neumann architecture have three buses.

• Data Bus - Carries data. This is bidirectional for read and write operations.
• Address Bus - This uniquely identifies which memory location is being read or written.
• Control Bus - This determines whether data is to be read or written. There are other control bus wires for handling interrupts and selecting memory or I/O ports.

Harvard Architecture

These chips have an extra instruction bus. This allows instructions to be fetched at the same time as data. This makes processing faster. This is known as the Harvard Architecture.

Fetch Execute Cycle

Microcontrollers

• low cost
• fairly simple to use
• easy to interface to transducers including sensors and control actuators
• versatile
• can be re-programmed for use in many different domestic and industrial control applications
• reliable (there are no moving parts)
• can interface to complex text or graphical displays

Benefit to Society

• domestic appliances become cheaper
• domestic appliances become more useful and versatile (programmable bread maker, washing machine, clock radio, DVD Recorder, etc)
• devices provide more information to the user (electricity meters can now display power usage in a visible location (not under the stairs). This allows users to save energy, money and the planet).
• car engine management processors save fuel, carbon emissions and reduce engine wear.

Inside Microcontrollers

The diagram above shows most of the features of a microcontroller.

Processor

• Fetches instructions
• Reads input data from memory and the input ports into the processor.
• Makes decisions
• Performs arithmetic
• Performs logic
• Writes output data to memory and the output ports.

Clock

• Synchronises all the operations within the microprocessor.

Memory (ROM, RAM, Flash)

• ROM: Read Only Memory.
  • Non Volatile - retains its data when the power is off.
• RAM: Random Access Memory
  • Volatile - data is lost when the power is off.
• Flash
  • Non volatile memory that can be erased and re-programmed

Input/Output Ports

• Used to connect the processor to the outside world.
• The processor WRITES to the port to send out control data.
• The processor READS input data from the port. This is also called polling.

Von Neumann Architecture

Three Buses

• Address Bus: Each memory location and I/O port is uniquely identified by its address. Setting the address activates exactly one memory or I/O circuit.
• Data Bus (Bidirectional): Carries data to the processor (read) of from the processor (write). Instructions and data have to be fetched in two steps. This makes this type of processor slower.
• Control Bus: Determines the read/write direction. Selects memory/IO. Carries the clock signal.

Harvard Architecture

Four Buses

• Address Bus: Each memory location and I/O port is uniquely identified by its address. Setting the address activates exactly one memory or I/O circuit.
• Data Bus (Bidirectional): Carries data to the processor (read) of from the processor (write).
• Control Bus: Determines the read/write direction. Selects memory/IO. Carries the clock signal.
• Instruction Bus: Carries the instructions at the same time as the data is fetched. This speeds up the processor.

Bus Widths - 2^N

The bus width is important. This is a 2ⁿ calculation. You can calculate ...

• The number of unique addresses is 2^N numbered from 0 to 2^N - 1.
• The largest number the bus can carry: 2^N - 1
• It the bus carries video data to a screen, the number of colours the screen can display
• If the bus carries data from a Gray code position sensor, the maximum number of positions that can be sensed

• 4 wire bus: 2⁴ addresses = 16. Largest possible number is 2⁴ - 1 = 15
• 8 wire bus: 2⁸ addresses = 256. Largest possible number is 2⁸ - 1 = 255
• 16 wire bus: 2¹⁶ addresses = 65536. Largest possible number is 2¹⁶ - 1 = 65535

Hardware and Software

Hardware

• Physical devices
• Needs a power supply
• Arrives in a box
• Installed with a screw driver, plugs and sockets or a soldering iron
• Breaks if you drop it

Software

• Programs
• Data
• Can be downloaded
• Stored on a disk
• Installed by running the setup program
• Can be copied
• Can be transferred across a network
• Can be lost if you don't make a backup

Firmware

• is software on ROM that can't be altered or on Flash Memory that can be re-programmed with suitable tools.

Wetware

• a nerdy term for processing data using a human or other animal brain.

Extreme Performance - Thanks XKCD

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