cEMI Bedeutung | (EMI1,EMI2)

[HFS45]

Hallo!

Was bedeutet eigentlich cEMI (Common External Message Interface ->sollte man vielleicht ins Wiki eintragen) genau? D.h. wenn man das Wörtchen cEMI in den Mund nimmt was meint man damit genau? Meint man damit den Aufbau eines EIB Telegramms (Steuerfeld, Quelladresse, Zieladresse, Routingzähler, Länge, Nutzdaten, Datensicherung), obwohl das wahrscheinlich nicht stimmt weil das ja nur der Telegrammaufbau von KNX über TP(Twisted Pair) ist? Das cEMI Format wird ja angeblich bei jeglicher KNX Telegramm Übertragung verwendet, unabhängig von der darunter verwendeten Technologie sei es über TP,Powerline,RF oder IP.

Was ist also genau gemeint mit cEMI und was sind EMI1 und EMI2 (hab ich mal irgendwo gelesen das es die auch (gibt) gegeben hat), sind das Vorgänger die es gab als es KNX noch nicht gab??

Mit bestem Dank im Voraus Harald

[S. De Bruyne]

EMI1 was the message format that was used by the BCU 1 on PEI 16 in your RS232 interface.
EMI2 was the message format that was used by the BCU 2 on PEI 10 in your RS232 interface.

Now, both protocols were not so flexible, for e.g. transferring frames of LTE (LTE-HEE, HVAC, Synco...) or Powerline and Radio Frequency.
Moreover, EMI1 and EMI2 do not have an explicit management of the interface.

Therefore, cEMI was invended.
It is flexible, with optional fields, and should thus be more future proof.
It is thus amongst other capable of transferring LTE-frames, RF-frames, etc.
Moreover, it comes with an explicit model for managing the interface, with own services for managing the interface.

cEMI has also been used as the tranport format on IP (KNXnet/IP).
For interfaces to TP, RF or PL, the interface indeed has to convert between the generic cEMI frame format and the frame format on the given medium.

[HFS45]

Hallo!

Danke erstmal für dein Erklärungen, nun weiß ich wie cEMI , EMI1 und EMI2 zusammenhängen. Ich weiß aber leider noch nicht was EMI (External Message Interface) eigentlich ist, das ist aber, glaube ich, am allerwichtigsten.

Was ist EMI, was macht es, wo kommt es im übertragenen Bytestrom vor?

MFG Harald

[S. De Bruyne]

Was ist EMI

EMI is the specification of the format of KNX messages when they are transferred over RS232, USB, IP.
It looks strongly like the format of the bus, but is a little different.
EXAMPLE When a normal message is transferred and the EMI user (ETS, visualisation tool) has connected to the Data Link Layer interface of a BCU 1, the EMI 1 message starts with a message code (a hex value that says that it is an L_Data.req; other messages, e.g. from Transport Layer have a different code), then the Ctrl-field (more or less the same as on the bus), then 2 bytes void (were the source address used to be), then the destination address, the NPCI (address type, routing counter; as on the bus), and the rest of the frame (as on the bus). Note that the checksum for instance is not contained in the EMI 1 frame format.

was macht es

Es macht an sich eigentlich nichts.
It is the RS232 or USB interface that transfers the messages; EMI is only the definition of the format.

wo kommt es im übertragenen Bytestrom vor?

That depends on the host protocol, that means, it looks different on PEI-type 10, on PEI-type 16 and on USB or IP. But somewhere in the stream of these protocols, the EMI-message starts, e.g. in the above example, you will see some bytes from the host protocol (e.g. total length) and then the message code, ctrl-field, etc.
I do not know whether this is clear, without giving really the specifications. Feel free to reply.

[Warichet]

Thank you for taking the time to post this information.

I appreciate arcitectural details, especially when they are put in perspective by an example.