Transmission theory of X-10 signals
The X-10 communication is based on the "injection" of high-frequency signals (120 kHz) on the 220Vac network, representing binary signals (1 or 0). The signal is inserted immediately after the passage through the origin of the sine wave of 50Hz, with a maximum delay of 200 microseconds. This special feature is used by receivers to know when to listen to the line. The signal is sent through the electric energy network to the X-10 receivers connected to the network.
To allow the use in three-phase electrical networks, the 120 kHz signs are transmitted three times in each cycle, in moments that coincide with the passage of zero voltage of each of the phases. Thus, using its own couplers, it is possible to communicate with any device, regardless of the phase in which it is installed. In order to simplify the explanation, this fact will be omitted in the continuation of the text, referring only to the signals of a single phase.
|Sine wave with the injection of an X-10 signal
Since the means of distribution of energy is electrically very noisy, a policy in which a bit is never sent alone was adopted, and the bit is always sent together with its complement. In practice this means that whenever you want to send the bit 1, it corresponds to sending a 1 (120kHz sign at the source) followed by a 0 (lack of signal). The sending of bit 0 corresponds to send a 0 (lack of signal) followed by a 1 (120kHz frequency at the source). This is illustrated in Figure 3. This aims to minimize the probability of the electrical noise being confused with a valid signal. However, it has disadvantage of reducing the rate of transmission, which is thus restricted to a mere 50 bps (a bit is sent per cycle of the electricity network).
|Sending of binary signals 1 and 0
A complete transmission of an X-10 command includes the transmission of four fields that "occupy" eleven cycles of the electric wave. The first field (2 cycles) represents the "Start Code" - sequence of bits (1 1 1 0). It should be pointed out that this is the exact sequence indicated and that the rule of each bit being followed by its complement is not confirmed. The following field, represented by 4 cycles, presents the home code and their respective supplements. Similarly 4 more bits are followed, which occupy 4 cycles that represent the device code or the code of the function. In order to distinguish this last field a bit is sent (and its respective supplement), which identifies whether the previous field refers to the number of a unit (bit = 0) or to the code of a function (bit = 1).
Each complete package must be sent in two groups (the first to indicate the device and the second the function to be executed) with a maximum of three cycles of the sine wave alternating between each group. The commands Dim and Bright are exceptions to this rule and should be continuously transmitted without a cycle interval between them.
|Example of the transmission of an A2 ON command
An X-10 command usually includes two actions: activate a particular device (message code indicating device), and then send the function to be executed (message with the function code). Note that after a certain device is activated, it will remain active until another is located. While a device is active you can send it multiple commands.
|0 0 0 0
||All Units Off
||Switch off all devices with the house code indicated in the message
|0 0 0 1
||All Lights On
||Switches on all lighting devices (with the ability to control brightness)
|0 0 1 0
||Switches on a device
|0 0 1 1
||Switches off a device
|0 1 0 0
||Reduces the light intensity
|0 1 0 1
|| Increases the light intensity
|0 1 1 1
|1 0 0 0
||Requests a response from the device(s) with the house code indicated in the message
|1 0 0 1
||Response to the previous command
|1 0 1 x
||Allows the selection of two predefined levels of light intensity
|1 1 0 0
||Additional data (followed by 8 bytes)
|1 1 0 1
||Satus is On
||Response to the Status Request indicating that the device is switched on
|1 1 1 0
||Status is Off
||Response indicating that the device is switched off
|1 1 1 1
||Request requiring the status of a device
The previous table describes all commands supported by the standard X-10. The first six are the basic commands more frequently used. It should be pointed out that the use of the Dim and Bright functions are not restricted to the regulation of the light intensity and can also be used for other functions, such as rolling the blinds up and down or controlling the heating.
The Hail Request and Hail Acknowledge functions are used to determine whether it is possible to communicate with a house nearby. If this situation occurs, it is necessary to use a different home code or a filter, which prevents the X-10 signals circulating to other houses. The Extended Code and Extended Data functions are introduced in the X-10, in order to send more commands or additional data.