X10 Protocol: Home Automation Technology Basics

This page covers the X10 protocol and X10 Home Automation Technology basics. The X10 protocol describes home automation concepts of X10 signal, X10 packet format, and X10 Physical layer.

What is X10 Powerline Technology?

X10 is a protocol that helps IoT devices communicate in the home automation sector. IoT stands for the Internet of Things, which is a system of interconnected objects through the internet. Such IoT devices are called smart devices. The X10 is a powerline signaling technology invented in the year 1970.

The existing wiring of a household acts as the transmission medium to transmit and/or receive data in an X10 system. The X10 devices are connected to the wall similar to electric switches and boards. The X10 devices are controlled using remote controlled devices based on the following X10 protocol format.

X10 Home Automation Technology

Let us understand the protocol format of X10 powerline technology used in IoT home automation. This technology supports 256 different X10 devices on a single powerline. This is because an X10 device can have one of 16 possible house codes (‘A’ to ‘P’) and one of 16 possible unit codes (‘1’ to ‘16’). A total of 16 command codes are defined in X10 technology. The most common among them are ON, OFF, DIM, BRIGHT, ALL UNITS OFF, and ALL LIGHTS ON.

Following are the basic features of X10 technology.

Table-1: X10 Home Automation Technology Features

X10 Protocol Structure | X10 Signal, X10 Packet, X10 Physical layer

Figure-1: X10 Signal Waveforms

As mentioned in table-1, X10 Physical layer (X10 PHY) uses OOK modulation and Manchester coding to represent binary information. The figure depicts the X10 signal. The X10 system transmits one-bit information at each powerline zero crossing.

A burst of 120 KHz having a duration of 1ms designates as binary ‘1’ bit and the absence of carrier designates as binary ‘0’ bit. Both INSTEON packet and X10 burst are depicted at each zero crossing in fig-1. INSTEON packets begin 800 µs before a zero crossing and last until 1023 µs after the zero crossing. The X10 signal uses a burst of approximately 120 cycles of 120 KHz carrier beginning at the powerline zero crossing and lasting about 1000 microseconds. A burst followed by no burst signifies an X10 one symbol and no burst followed by a burst signifies an X10 zero symbol.

An X10 message begins with two bursts in a row (a start symbol), followed by a one symbol, followed by nine data symbols. The figure shows an X10 burst at each of the two zero crossings.

X10 packet = { Start Code(4bit), House code(8bit), Key code(10 bit) }

Each X10 packet is sent twice followed by 6 zero crossings of silence period before a new packet is transmitted. In certain X10 commands such as BRIGHT or DIM silence interval is not used. The Start Code will always be ‘1110’ and the rest of the packet consists of a complementary pair of bits (Either 01 or 10 and never 00 or 11).

If the key code ends in ‘01’, the first 8 bits are treated as a unit code. If the key code ends in ‘10’, the first 8 bits are treated as a command code.

The table-2 mentions 16 possible combinations of 8 complementary bit fields which are interpreted into different (House Code,Unit Code,Command Code) fields.

Table-2 : X10 packet fields (House Code, Unit Code, Command Code)

EXAMPLE of X10 protocol Packet which will turn ON module-A1 in HOUSE-A.

{1110(Start),01101001(House A),0110100101(Unit 1)} {1110(Start),01101001(House A),0110100101(Unit 1)} {000000(Silence)} {1110(Start),01101001(House A),0101100110(Command On)} {1110(Start),01101001(House A),0101100110(Command On)} {000000(Silence)}

One bit in X10 packet is transmitted each time the 60Hz powerline voltage crosses zero. This occurs in every 8.33 milliseconds time period. There are 100 bits in a packet and hence the entire sequence takes 833 milliseconds to be transmitted.

Though this technology is obsolete, it is widely used in its successor technology known as INSTEON.