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Chapter 2. Related Work/Fundamentals 16

systems, above all to Asian products, where this IC is widely used due its low cost. This makes

it possible to upgrade an automation system with non-Intertechno devices. Nevertheless, reliable

cooperation cannot be guaranteed.

IT devices form loosely connected networks, in which transmitters are normally linked to just one

or two receivers. Due to the manual addressing, each device can theoretically be connected to an

inﬁnite number of counterparts. Data transmission is unencrypted and OOK modulated within

the 433.92 MHz band. Devices can either send or receive, thus the transfer is unidirectional. To

increase reliability of reception, commands are sent four times, whereof at least two messages

must be received for successful switching. The range is comparatively small with only 30 m (line

of sight), but can be increased with a repeater.

Protocol There are two diﬀerent protocols: The open protocol of the HX2262 and the newer,

proprietary protocol of self-learning devices. The latter one will not be examined further in this

work.

The protocol is generated by the HX2262 IC. By pulling the enable-pin to Vss, the IC transmits

sequentially the states of its 12 inputs and a synchronization pulse, which serves as a spacer for

subsequent repetitions. Each state is composed of two pieces of data, each lasting for four cycles

(ﬁgure 2.10). A synchronization pulse corresponds to the data element 0, which was extended to

32 bars. The cycle time is 400 µs.

Data „0”

Data „1”

Figure 2.10.: Data elements 0 and 1.

An address pin can assume three diﬀerent states, whereas a data pin can only have the state Vss

and Vcc. The state ﬂoat means that the input is neither Vss nor Vcc, but it is unconnected. Float

is represented by 01 (see ﬁgure 2.11 on the next page).

A data package consists of 25 bits, consequently a single transmission lasts 51.2 ms and a full

transmission of four packages needs 204.8 ms. On the receiver side, incoming data streams are

shifted into the input of the HX2272 and the received address is compared to the internal one

with each occurrence of a syncbyte. If both are the same, the data pins are set according to the

received ones.

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