====== Debounce ======
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This function works only for following Inputs & Outputs: 
  * **digital inputs**
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===== How it works =====

The **debounce** functionality is for catching glitches which typically occur when changing states on the digital input. Those happen mostly when the digital input is operated by some mechanical element, e.g. momentary switch. The signal generated upon pressing and releasing a momentary switch can look like this:

{{ .:debounce:debounce_00-bounce-example.jpg?direct&400 |}}
Note that the bounces shown above are exaggerated and typically are measured in hundreds of μs.

To "debounce" these glitches, you have to slow down the reaction on changing states of the input. On HW level you could achieve this by employing an RC element. To make your life easier, you can set this "slowing down" on SW level. We will call "debounce time" as the smallest period between rising and falling edges, after which change can be acknowledged as valid. Impulse (rising edge) is processed as valid only in case it equals logical 1 for the whole debounce time duration.

/*The functionality looks for changes on a digital input. If the change is less then defined debounce time, it will be ignored. Once the change exceeds the debounce time, then the event is passed to the Mervis.*/

/*FIXME //je to zmíněno již niže, ale zde bych to taky říkal, že je debounce nastavený by default a na hodnotu 5ms. Potom bude nadpis s changing dávat větší smysl//*/

===== Changing the debounce time =====

Now let's see how **debounce** can be configured in the Mervis IDE. The **debounce** settings can be found in device inputs, so right-click on the name of your Unipi controller under the Modbus TCP channel and select Open Editor. A tab with all controller registers will appear. 

{{ .:debounce:debounce_01-open-controler-definition.png?direct |}}

Under the Name field, you will find a search bar in which you enter ''DI_''. A list of all available digital inputs, or more precisely their data points, is displayed.

{{ .:debounce:debounce_02-register-search.png?direct |}}

Select one or more desired digital inputs, for which you want to change the debounce time. In the **Properties panel** you can see all the options you can set on these registers. The option we are interested in right now is the **Debounce**. The value of this option is represented in ms(milliseconds) of deboucing period. 

/*FIXME //Dá se debounce vypnout? Předpokládám nastavením hodnoty debounce na 0.//*/

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**Note:** \\
All digital inputs are set to 5 ms debounce time by default, which means **digital inputs** will ignore changes shorter than 5 ms.
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{{ .:debounce:debounce_03-debounce-property.png?direct |}}

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**Important:** \\
We just changed the configuration of the PLC modules, which is not applicable by simply uploading the solution. To save the configuration, follow the [[en:sw:01-mervis:unipi-configure-module-hidden|Unipi - Configure Module]] tutorial.
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