The Internet Power Line Adapter - University of Queensland

Home Automation, Power Lines and the Internet Quenten Alick
A complete X-10 takes 11 AC cycles to transmit. The header code (1110) is
transmitted during the first two AC cycles with one bit transmitted per half
cycle. The next eight cycles are used to transmit eight data bits, with each bit
being transmitted both “normally” and complemented. This is similar to
Manchester Encoding and is used to make to signal more resistant to line noise.
The first four bits are the house code and the second four are the unit code.
Finally, a stop bit is transmitted in the 11 th AC cycle.
Once the 11-cycle transmission has been completed, the transmitter goes idle for
at least three AC cycles before it repeats the same transmission. After the repeat
transmission, a signal can be sent that will tell the addressed device what it has
to do, for example for a light, turn on or off. This message must also be
transmitted twice. The formats of the two messages are shown in figure 2-2.
Start code (4 bits) House code (4 bits) Unit code (4 bits) Stop bit (1 bit)
Start Code (4 bits) House Code (4 bits) Control (4 bits) Stop bit (1 bit)
2.2.3 X-10 Summary
Figure 2-2 X-10 Transmission Formats
Although the X-10 system is widely used and already has many products on the
market, there is one main drawback to the system. Despite all the redundancy in
the transmission of information, the signal is still very susceptible to line noise. In
many cases, repeaters or noise blocks / filters (to remove the effects of high
capacitance power loads such as computers) need to be added before the home
automation system functions reliably.
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