PROGRAMMABLE INTERFACE CONTROLLERS

1
PROGRAMMABLE INTERFACE CONTROLLERS

• Understanding what PICs are.
• How to use PIC logicator
• Knowing what you can do with PIC circuits

2
What a PIC does

• PICs allow you to control output devices when
  they are triggered by sensors and switches.
  Programs can be generated by using flowcharts
  within computer software, which can then be
  downloaded into a PIC chip. They can be
  re-written as many times as you want. This type
  of memory is called flash memory.

3
Inside the PIC CHIP

• A PIC microcontroller is a single integrated
  circuit small enough to fit in the palm of the
  hand and contains memory processing units, a
  Clock and Input/ Output circuitry in a single
  unit. A PIC microcontroller is ,therefore, often
  described as a computer in an integrated circuit.
• PIC microcontrollers can be purchased blank and
  then programmed with a specific control program.
• PIC microcontrollers can also be purchased with a
  pre-programmed set of commands that allows a
  direct cable download from a computer and reduces
  the cost of programming equipment.

4
Advantages/Dis-advantages of PICs compared to a
555 Timer flashing circuit (astable)

• PIC allows greater control.
• Pattern can be tested on PC before build
• PIC can be programmed to produce different
  patterns
• Limited output from 555 Timer IC
• PIC requires fewer components
• PIC more costly than 555
• PIC possibly smaller PCB
• PIC requires programming skills

5
PIC TASK (EXAM QUESTION)

• Using a programming system you are familiar with,
  produce a sequence of commands, which would make
  a set of 4 LEDs, shown in Figure 3, switch on as
  shown below
• Next to each of the commands, explain its
  purpose.
• All four LEDs go high for 1 second.
• A, B, C and D go high in sequence, each for 0.25
  seconds.
• All four LEDs go high for 1 second.
• D, C, B and A go high in sequence, each for 0.25
  seconds.
• This repeats continuously.
• Between each statement, all LEDs go low for 0.25
  seconds.

6
PIC TASK (EXAM QUESTION)

• Use a PIC to simplify the electronic circuit for
  a steady hand game
• The PIC system diagram is shown below
• Use a PIC program to satisfy the following
  conditions.
• Each time the wand and track touch, the PIC
  switches on an LED in the sequence 1, 2 and 3.
  Once an LED is lit it will stay on until reset.
  (9 marks)
• Once the wand and track touch, the PIC will
  ignore any further contact between the wand and
  track for 2 seconds. (4 marks)
• (c) On the loss of the third life, the buzzer
  will switch on for 0.25s and then switch off for
• 0.25s. This is repeated three times. (6 marks)
• (d) The PIC program will re-set back to no
  lives lost. (3 marks)

7
PIC TASK (EXAM QUESTION)

• The picture opposite shows a drawing of a lift
  with its doors open at the ground floor.
• The lift will only operate when a person has
  requested the lift from another floor, or a floor
  has been chosen by a person in the lift and the
  doorway is not obstructed.
• Design a flow chart to illustrate the lift
  operating sequence, from when the lift starts at
  the ground floor, with its doors open and is
  called to the first floor where its doors open.
  (10 marks)
• Quality of drawing (2 marks)