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Master ⁄ Slave
The telegram flow in the RS 485 network and the bus access respectively are not strictly regulated by the master (PC ⁄ PLC ⁄ controller)
only. There are telegrams being initiated by the radio frequency gateways (slaves) themselves that need to be acknowledged by the master
system.
On principle each telegram, no matter whether coming from the master or from slaves, requires to be acknowledged by the addressed
subscriber.
Bus conflicts ⁄ telegram repetitions
Bus conflicts have different causes. Some of which are e. g. a wrong type of cable used for the RS 485 bus cable, a subscriber device not
being connected or defective, or an incorrect baud rate has been set.
Bus conflicts are solved that way: when a reply or acknowledging telegram ACK in answer to a telegram (query or command) is missing,
the telegram is repeated up to two times. The intervals between two telegrams being repeated are at random between 500 and 1000 ms.
After the third attempt with a reply or acknowledging telegram ACK still failing to appear, the telegram will be rejected and the next
command is being processed.
Telegram types
The following table describes the telegram flow as well as possible telegram types
being specified by a byte type value (see telegram structure):
Flow direction .................. Value ........Description ..............................................................Comments
Gateway → Master ............ 0B .............RRT (Radio Receive Telegram) ............................A telegram from a radio transmitter was received by
the gateway and forwarded to the RS485 bus.
The telegram needs to be acknowledged by the master.
Master → Gateway ............ 6B .............TRT (Transmit Radio Telegram) ..........................A telegram that was sent from the master to
the gateway (addressed by the subscriber ID number).
The gateway will acknowledge the telegram and
transmit it in form of an EnOcean radio telegram.
Gateway → Master ............ 8B .............RMT (Receive Message Telegram) .....................A telegram from the gateway (addressed by
the subscriber ID number) to the master.
The telegram needs to be acknowledged by the master.
Master → Gateway ............ AB .............TCT (Transmit Command Telegram) ..................A telegram from the master to the gateway itself
(addressed by the subscriber ID number).
The gateway will acknowledge the telegram or
send a response telegram to the master.
Master
Gateway
Gateway
Possible types of transmission of a RRT telegram (type = 0B)
The telegrams from different radio transmitters are distinguished by a value in the ORG field.
These are:
Value .........Description
05 .............A telegram from a transmitter with PTM module
06 .............A telegram from a transmitter with STM module 1 byte
07 .............A telegram from a transmitter with STM module 4 byte
08 .............A telegram from a transmitter with CTM module
Detailed descriptions of the telegrams sent by different sensors are found in the respective sensors’ datasheets.
Telegrams in detail
See appendix for details. All possible telegrams that can be used under this current software release are listed there.
