science

Very Simple Control Protocol

Very Simple Control Protocol is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Very Simple Control Protocol rather than just read about it. In short: The Very Simple Control Protocol (VSCP) is a free automation protocol suitable for all sorts of automation task where building- or home-automation is in the main focus. Its main advantage is that each VSCP-node can work completely autonomous, being part of distributed network of other nodes.

Key takeaways

Very Simple Control Protocol belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Very Simple Control Protocol to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Very Simple Control Protocol from memory before moving on to harder problems.

Reference excerpt

The Very Simple Control Protocol (VSCP) is a free automation protocol suitable for all sorts of automation task where building- or home-automation is in the main focus. Its main advantage is that each VSCP-node can work completely autonomous, being part of distributed network of other nodes. VSCP is independent from the physical layer (e.g. CAN bus, Ethernet, RS-485, RS-232, MiWi) connecting the individual nodes to form the automation network bus. On the bus there can be nodes reading switches, controlling lighting, blinds, windows or information displays, broadcasting physical measurements (e.g. temperature, luminosity, power consumption, etc.), multimedia control, burglar- or fire-alarm, etc. There is a subset of the protocol (Level I) that is very much tailored to the CAN bus and resource restricted microcontrollers. Protocol Level II is designed for Ethernet (UDP, TCP and own Ethernet-type Raw-Ethernet) and wireless physical layers. All share the same common message fields and framework and can be connected through gateways.

Event VSCP is based on events. Each time an event occurs it is broadcast towards all other nodes. Each node on the network will receive the event and will decide if this event needs to be handled or not.

The example given in the diagram describes a button being pressed. This will result in node 1 sending an event message onto the bus informing all others the button is pressed. Node 2 receives the message but decides this button should not trigger an event for node 2. Node 3 receives the message and decides this button should trigger lamp 2 to turn on. There can be events for all sorts of things happening: an event can be a button pressed, a presence sensor being triggered, or the sun setting. Events can also be sent periodically, for instance a temperature reading every minute. VSCP predefines many events that could be happening. These events are defined into classes and types. Whether or not an event received should be handled is determined by the decision matrix or DM in short. Also the DM is explained further.

Event Class and Type Events are organized into Classes. A class is a collection of events that somehow belong together. There are classes for ALARM, MEASUREMENTS, CONTROL, INFORMATION, etc. Currently VSCP specifies about 25 classes, but has room for many more 1. Each class is on its turn subdivided into types. A type further specifies the event within the class. For instance, events of Class 20 (0x14) are INFORMATION events. In this class there is a subtype 1 (0x01) BUTTON signaling a button being pressed. In this same INFORMATION class there are also types to signal ON, OFF, BELOW LIMIT, etc. Likewise in class measurements there are types to signal temperature, current, voltage, etc. Having all these classes and types defined makes the nodes speak the same language. For a full list of pre-defines classes & types check the VSCP wiki.

VSCP event datagram structure Events that are broadcast contain a number of fields together forming one VSCP datagram. Exactly how these fields are mapped onto the physical layer is specified for a number of physical layer protocols such as CAN, Ethernet, TCP, etc. For others it is not yet defined, but it is in general not difficult to map these fields onto a physical layer protocol. There are 2 levels of the VSCP protocol called LEVEL I & LEVEL II. They are both basically the same protocol but differ in size of the different fields. Level I is intended to run on nodes with more constrained resources and fields are defined a bit more conservatively. Level I is in fact a subset of level II, and with an appropriate gateway events can transverse between a Level I & II network.

Level II is intended to be run on nodes that have little resource constraints and can easily cope with larger message sizes.

Decision matrix

When events are received by a node the node needs to determine if it needs to execute a task based on that event. This is done by evaluating the decision matrix or DM in short. The DM matrix is made of a number of IF ... THEN ... conditions. Each such IF/THEN condition is called a line and multiple lines make up the decision matrix. The Class and Type of the incoming message is always evaluated by a DM line. Evaluating Class & Type is done by passing the Class/Type through a mask first and then comparing with a filter. This method allows multiple class/Types to trigger a valid condition for 1 line of the DM. The other conditions for the DM line (SenderGUID, Zone, Subzone) are optionally evaluated. If the DM line is valid then the ACTION is executed. Together with the ACTION there is an ACTION parameters. An example ACTION would be: turn-on relay 6 with 6 being the action parameter. Exactly which ACTIONs are possible by the receiving node is determined by the design of the node itself. It is up to the firmware developer to define which actions can be executed. By then documenting the possible action in the MDF file (see later) the configuration SW will know how to select this action. The DM can be modified by setting the appropriate node configuration registers. A convenient way to do this is using the VSCPWorks configuration SW.

DataPayload An event being sent can also carry a data payload. The content & organization of this payload is depending on the class and type of the event. For example, an event of class 10 (measurement) and type 6 (temperature) will carry the temperature data (with coding determined by byte 0, degrees or Celsius) in its payload. A button event will carry information about the button & button zone/subzone in its datapayload. For each class/type the data formatting is determined in the spec, please consult the wiki for details.

Zone/subzone Some (quite some) events contain a field zone and a field subzone in their datapayload. This functionality is present to make grouping of nodes possible. For instance we could determine that all buttons controlling a certain lamp are part of the same group. This simplifies the DM for certain scenarios. Instead of having one DM line as the lamp node for each button (1 line per button: IF button x then turn-on lamp) we could have 1 DM line only saying IF (zone match) THEN turn-on lamp. Making multiple node switches part of a group is done by configuring the nodes, the firmware of the node will support this functionality.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Very Simple Control Protocol

Start with the simplest possible case. Write down what Very Simple Control Protocol claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Very Simple Control Protocol before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Very Simple Control Protocol ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Very Simple Control Protocol

In research: Very Simple Control Protocol appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Very Simple Control Protocol in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Very Simple Control Protocol is common in secondary-school and first-year university syllabi. It links to neighbouring topics Building automation, so understanding it makes those chapters shorter.
In everyday life: Look for Very Simple Control Protocol outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Very Simple Control Protocol in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Very Simple Control Protocol means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Very Simple Control Protocol out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Very Simple Control Protocol in simple terms?

Why does Very Simple Control Protocol matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Very Simple Control Protocol?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Very Simple Control Protocol.