Exercise - Configuring Icons and Variables
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- 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.)
- 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.)
- 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:
- 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.
- 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.
- 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.)
- 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.