Microcontrollers: A family of integrated circuits that contain all the sub-systems needed to make programmable control systems.

Programmable Integrated Circuit or PIC Microcontrollers

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.

This PIC board is home made and based on the PICAXE manuals. It uses the PICAXE 28X1 chip which runs the AQA assembly code instruction set.

PICAXE Board

The AQA processor allows 8 bit I/O on PORTA, PORTB and PORTC.

The PICAXE 28X1 processor is slightly different ...

  • PORTA: This port exactly matches the AQA processor.
  • PORTB: This port is restricted to output only.
  • PORTC: This port is missing on the PICAXE chip.
  • There are four additional ADC input ports (not on the AQA specification).

PIC chips are useful because ...

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

The chips benefit society because ...

  • 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.

This is a "System on a Chip". All the required components are fabricated onto a single piece of silicon, The chips contain ...

  • a processor
  • a data bus, instruction bus, address bus and control bus
  • ROM - Memory that contains code that never changes.
  • Flash RAM - Memory that retains its data with the power off but can be re-programmed)
  • RAM - Memory used for temporary storage
  • Input/Output (I/O)
  • Some chips have DAC and / or ADC circuits

Here is a simplified summary of the PIC chip.

PIC Architecture

You can download the data sheet for the PIC16F886 from microchip.com.
This is the chip used for the PICAXE 28X1. This chip does not include the PICAXE software.
The PICAXE 28X1 chip has been programmed to include the PICAXE software needed to run PICAXE BASIC.