KTX2_12 データシート(Datasheet) 3 Page - Radiometrix Ltd
RADIOMETRIX [Radiometrix Ltd]
Radiometrix Ltd, KTX2 Data Sheet
Notes on the KTX2:
The Module will transmit if any of the function lines (S0 – S3) is activated (high).
Single message time is typically 150ms.
Whilst S0 – S3 are all deactivated (low) standby current consumption is <1uA.
The Module will transmit the same message (with the same hop-code) repeatedly whilst any of the
function lines are held active high, until power-saving time-out occurs after approx. 30s.
When the power-saving timeout occurs, current consumption will be <350uA, until all function
line(s) are released again.
Whilst a function line is held high, if another function line is taken high then the function code in the
message changes to reflect the new state of the function lines and the hop-code is also changed –
as if the user had released all function lines and activated the new combination.
Releasing individual function lines (whilst at least one function line remains high) has no effect on
the transmitted message.
The supply monitoring status bit is set when module supply drops below 3.8V (approx.) and resets
when supply falls even further – below 2.2V (approx.) – but note that this is less than the minimum
supply recommended for use with KTX2.
Description of the KTX/KRX code hopping system:
Every time a function code is activated causing KTX to transmit, a hop-code is generated. The hop-code is an
encryption based upon a Manufacturer code and the module ESN (unique to each module). An encryption
algorithm uses these two variables to generate the hop-code, which will change for every new transmission.
Note that the data itself (i.e. the function code) is not encrypted, as it is the identity and status of the sender that
is used to safeguard operation of the system.
At the KRX receiver-decoder, the hop-code can only be decrypted with the correct key. The key is derived from
the manufacturer code and the KTX serial number. The manufacturer code is not transmitted: it is pre-
programmed into the decoder. Because the hop-code is changed for every new transmission the receiver
decoder must be synchronised to the transmitter encoder. This is achieved by “learning” the transmitter to the
receiver during which the serial number and synchronisation data is stored in the receiver-decoder.
Transmissions received from all KTX modules are decoded, but not acted upon unless the serial number has
been learned first and the decoder is synchronised to the encoder.
If the Radiometrix KRX decoder loses synchronisation with the transmitter (e.g. repeated transmitter activation
whilst out of range) then the KTX module must be activated twice before the decoder will allow the control to be
processed, but only if the KTX module is within a forward window of +32768 activations. This mechanism
prevents “code-grabbers” from breaking the security of the system by recording and re-broadcasting old codes.
Additionally, in the KRX decoder a window exists allowing up to 14 transmissions to occur whilst the transmitter
is out of range before two valid sequential transmissions are required to use the system. In practice a user may
not notice the latter, since human reaction to an unsuccessful attempt is simply to “press the button again”.
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