Exercise - Configuring Icons and Variables

Input

• Double click on the Input icon.

This opens the 'Properties: Input' dialogue box, allowing you to configure the way the program treats information from the switch.

This information will be contained in a variable called 'switch'.

• Click on the down arrow at the right-hand end of the 'Variable:' box to open the variables dialogue box.
• Hover to the left of the 'Variables' label and click on the down arrow that appears.
• Click on the 'Add new' option to open the 'Create a New Variable' dialogue box.
• Create a new variable named "switch" with initial value "0" and description "Copies the state of the switch"
• Leave the 'Variable type:' as 'Byte'.

(For more information about variables, see Creating Variables and Variable Types.

(The resulting dialogue box is shown opposite.)

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• Finish configuring the input properties as follows:

• Change the 'Display name:' to "Read the switch".
• In the 'Variable:' box, type the name of the variable you created "switch".
• Leave the 'Port:' as PORT A.
• Select to 'Input from:' 'Single Bit' and choose bit 0.

(The resulting dialogue box is shown opposite.)

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Set up like this, the program monitors the state of the switch, which will be connected to bit 0 of Port A of the microcontroller.

When the program looks at the input switch if it is pressed, the variable 'switch' contains logic 1. If unpressed, it contains logic 0.

Check the Switch

• Double click on the Decision icon to open the configuration dialogue box, and then:
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• Rename it "Switch pressed?".
• In the 'If:' box, type "switch=1".
• Leave the 'Swap Yes and No' box unchecked.
• Click on 'OK'.

This icon will be used to make the program perform what is known as a conditional branch.

The subsequent course of the program depends on the outcome of the condition specified in the 'Decision' icon.

In this case, it depends on whether or not the variable 'switch' = 1.

If it is, the program follows the 'Yes' route. If not, it follows the 'No' route.

Control the Lamp

The 'No' branch is easy to set up. All we want is that the program returns to the beginning (taken care of by the 'Loop' icon.)

No further configuration is needed.

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• Double click the 'Output' icon to open the configuration dialogue box, and then:

• Change the 'Display name:' to "Switch on".
• In the 'Variable or value:' box, type value "1".
• Change the 'Port:' to PORT B.
• Select to 'Output to: 'Single Bit' and choose bit 0.
• Click on 'OK'.

(The resulting dialogue box is shown opposite.)

The effect of this icon is to send a logic 1 signal (high voltage) to the lamp, connected to Port B, bit 0 of the microcontroller.

This turns on the lamp.

Now, we tackle the requirement that it stays on for ten seconds and then goes off.

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• Drag and drop a 'Delay' icon after the 'Output' icon.

• Double click on it to open the configuration dialogue box, and then:

• Change the 'Display name:' to "For 10 seconds".
• Change the 'Delay value:' to '10'.
• Change the unit to 'seconds'.
• Click on 'OK'.

(Again, the resulting dialogue box is shown opposite.)

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• Double click on the second 'Output' icon to allow you to configure it.

Rename it "Switch off", and configure it to deliver value "0" to single bit 0 of Port B.

The resulting dialogue box is shown opposite.

Finally, we need to turn off the lamp, after the ten second delay.

To do this:

• Drag and drop a second 'Output' icon after the 'Delay' icon.

You should now save the flowchart as "Lamp1.fcf", and close Flowcode.

What next

The next step is to add the switch and lamp to the flowchart. This is covered in the exercise Adding Devices to a Program.