User's Manual

USER MANUAL

PTM 210 / PTM 215 / PTM 215U / PTM 215J

DC Step code and later

The RLC counter is internally restarted to 0x0 once the AES key was changed via the NFC

interface.

After executing a factory reset (see chapter 3.4 for details), the PTM module returns to using

the factory set security key but does not reset the RLC counter associated with the key. The

last used RLC value associated with the factory security set key will be used.

3.2.1 Implicit RLC – legacy, not recommended

This mode is relevant only for the European market (868 MHz) because of certain legacy

receivers. For the J and U market 928 MHz and 902 MHz, there are no such legacy receivers

and thus this mode is completely deprecated in these markets.

The initial RLC counter value is transmitted from PTM 21x to the receiver only as part of the

teach-in telegram. Subsequent secure telegrams do not include it. Therefore, receiver has to

automatically increment its counter at every received telegram to keep it synchronized with

the PTM Module.

When telegrams are not received by the receiver then this may lead to a de-synchronization

of the RLC counter in the PTM module and the RLC counter in the receiver, i.e. the PTM

module counter will have a greater value than the receiver counter.

In order to mitigate this issue, the receiver will usually test the received rolling code against

a defined number – a window - of future expected rolling codes. If a RLC from within the

window can be validated then the receiver will resynchronize its counter automatically to the

new value.

The size of this rolling code window is defined on the receiver side.

For the correct function it is essential that the number of consecutive, non-received telegrams

does not exceed the size of this window.

3.2.2 Explicit RLC – recommended

This is the recommended secure mode for all frequencies and new applications.

In this mode the PTM module sends the RLC value as part of every data telegram. With

transmission of the RLC in every data telegram a desynchronization of the RLC counters

between receivers and transmitter like described above cannot happen.

The receiver uses the RLC value inside the radio telegram to decrypt and authenticate the

received message. The receiver has to check if the received RLC is higher than the last known

value and he does not have to apply any RLC window search mechanism.

3.2.3 Security Teach-in

The Security teach-in includes required information for the receiver to decrypt future data

communication. A security teach-in telegram is sent by PTM 21x after: