Now let’s look closely at the demo project that opened up when you started the IDE. It blinks the LED connected to pin 13 of your board. Many boards have a built-in LED on that pin, but let’s make it more clear by building a simple circuit:

Make sure you’ve uploaded the program to the board and the LED actually blinks.

Why does it blink?

The nodes

You see three nodes linked together in a chain to implement the blinking. Nodes are basic building blocks in XOD. Each of them handles a tiny portion of work and communicates with other nodes.

Let’s talk about each node one by one from bottom to top.

digital-output

This node represents a single physical output pin on the board. It can be either in a high (enabled) or low (disabled) state. We use it to switch our LED on and off.

The node has two inputs. They are PORT and SIG.

The PORT defines what physical pin corresponds to the node. Select the node by clicking on it. You’ll see the Inspector sidebar with the properties of the selected node, i.e. our digital-output.

Note that the PORT value is set to 13th pin.

The value on the SIG input defines whether the digital output port should go into a high or low state. In the Inspector, you see its value is disabled and has the placeholder “linked”. That’s fine, because the value is defined by a linked upstream node. More on that later.

flip-flop

This node is like a virtual light switch that can be turned on (SET), turned off (RST) or toggled (TGL).

In addition to its inputs, the flip-flop node has an output. It’s MEM, which provides the current state: high or low.

clock

The clock node emits a pulse on its TICK output at equal time intervals. The interval is defined by the value of the IVAL input.

Select the clock node and note the value set for IVAL in Inspector. The interval is expressed in seconds.

The second input, RST may be used to reset the clock. We don’t need this function in our program, so we don’t link it to anything.

The links

You see that nodes' inputs and outputs are connected together with lines. These lines are called links in XOD.

They make it possible for nodes to talk to each other. Upstream nodes produce values and downstream nodes consume that values.

What happens in our blink program? Take a look:

The clock node ticks at regular intervals
Each tick pulse goes to the flip-flop and toggles its state
The flip-flop provides its state value to the digital-output

As a result, we see the LED blinking.

Tweaking the program

Try to change something.

Select the clock node and set a different IVAL value, e.g. 1.0 second, upload the updated program and observe the result.

That’s not too interesting. Let’s add another LED. Improve your circuit:

Place a new digital-output node. To do this, use the Project Browser sidebar. The digital-output node is available in the xod/core library. Hover the cursor over the item and click the (+).

Alternatively, you can double click the workarea, press I, or hit Edit → Insert Node. It would open a quick search dialog. Start typing digital-input as the search query and you will quickly find the node you’re looking for. Press Enter or double click on an item found to place it.

You’ll see a new node appear in the main workspace. Drag it to the slot you want. The one next to the existing digital-output would be fine. In Inspector, set the PORT for the new node to 12, since it will control our new LED.

Now we need to provide the new node with data. Link its SIG pin to the flip-flop output:

Upload the updated program to the board. Whoa! Both LED’s are blinking.

Now let’s improve our program some more and make the lights blink alternately. To do this, we need to add a signal inversion into either of links connecting the flip-flop and digital-outputs.

The not node under xod/core does exactly that. Delete the existing link, place a not node, and add new links so that the signal from our flip-flop to the digital-output goes through it:

Upload the new version to the board. See the result?

Disjoint graphs and independent tasks

In XOD, nodes do not have to be connected in a single circuit. You can build two or more disjoint clusters of nodes to perform several tasks simultaneously.

Try adding yet another LED with an absolutely independent blink interval and state:

Now we have three digital-output nodes. It can be hard to understand which node corresponds to each LED, so it would be better to give them clear labels. To set a custom label for a node, select it and provide the label via Inspector:

You can provide a custom label for any node. Now the program looks clearer:

What’s next

You’ve seen pins and links that carry values of different types. Some provide logical values (high or low) and some transmit pulses (ticks). They are differentiated by colors. XOD has even more data types. Go to the Types and Conversions chapter to learn more on this topic.

README.md Unescape Escape

Nodes and Links