Why are time delays needed in PIC programs?

A PIC executes instructions in microseconds, far too fast for people to see. A delay, such as wait 500 ms, lets an LED flash visibly or a motor run for a set time.

Describe a flowchart that flashes an LED on and off once a second, forever.

The LED output is switched on, then a 0.5 s delay follows. The output is switched off, another 0.5 s delay follows, and the arrow loops back to the start.

What does increment mean in a PIC program?

Increment adds 1 to a variable, such as a count of people passing a sensor. Decrement subtracts 1.

CCEA A-Level Technology and Design 8900

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Microelectronic Control Systems

PIC flowcharts and programming

3 things to know
A2 1

Overview

Flowchart symbols, loops and delays, incrementing and counting, a car park program, subroutines, interrupts against polling, setting outputs in binary, simulation and debouncing.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

What do the start/stop, process and decision symbols in a flowchart show?

Key term

What does an input/output symbol represent in a PIC flowchart?

Key term

How is a continuous loop shown in a PIC control program?

Questions from this subtopic

Each one with the model answer underneath.

1
What do the start/stop, process and decision symbols in a flowchart show?
Model answer
A rounded start/stop box marks where a program begins or ends. A rectangle is a process, and a diamond is a yes/no decision.
2
What does an input/output symbol represent in a PIC flowchart?
Model answer
An input/output box reads an input pin or sets output pins high or low. The symbol links the program to the physical world.
3
How is a continuous loop shown in a PIC control program?
Model answer
The final arrow returns to an earlier point, so the sequence repeats until the power is removed. Most control programs run in such an endless main loop.
4
Why are time delays needed in PIC programs?
Model answer
A PIC executes instructions in microseconds, far too fast for people to see. A delay, such as wait 500 ms, lets an LED flash visibly or a motor run for a set time.
5
Describe a flowchart that flashes an LED on and off once a second, forever.
Model answer
The LED output is switched on, then a 0.5 s delay follows. The output is switched off, another 0.5 s delay follows, and the arrow loops back to the start.
6
What does increment mean in a PIC program?
Model answer
Increment adds 1 to a variable, such as a count of people passing a sensor. Decrement subtracts 1.

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