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Tomas Muehlhoff edited this page Sep 14, 2025 · 6 revisions

A RS485 device connected to the A/B RS485 port EBV Ceta 104 (likely other models as well) will receive following 26-byte datagrams every ~2,5 seconds. The project I took as base is https://github.com/bogeyman/gamma/wiki/Protokoll, but it's on the Gamma Model and describes the protocol between the base and the according remote control, so it deviates a lot. I also took https://github.com/phiresky/ebv-theta-to-mqtt as reference.

Example: 210a0a841700110000013e01af009401be0100800d00be01176d

I collected quite some samples, brought them into graphs, compared values with values I read of the display of the Ceta device and came to some conclusions. Unfortunately I didn't yet find all expected information, here comes what I have:

All datagrams are 26 byte long and sent in Hexadecimal, for the ease of displaying it, everything below is in Decimal. Byte offsets are marked with #

  • #0...#2: unknown, most likely start marker, seem to be always 210a0a ?
  • #3...#4: unknown, most likely message type, seem to be always 8417 ?
  • #5...#7: unknown, message length seem to be always 0011 (=dec 17= 26 bytes total - 7 bytes header - 2 bytes checksum)

....

  • #8: 0,1 unknown
  • #9: unknown, seem to be always 1
  • (#10+#11*256)/10 (long int):
  • (#12+#13*256)/10 (long int): Nominal Temperature Water
  • (#14+#15*256)/10 (long int): Actual Temperature Burner
  • #16: duplicate of 15?
  • #17: "Burner mode (0=off, 1=heat, 2=water, 128=?)" ?
  • #18: unknown, always 0
  • #19: unknown, always 128 (or 1000000, so it could be bit-coded, still it always remains the same)
  • #20+#21*256)/10 (signed long int): Outdoor Temperature
  • #21+#22*256)/10 (long int): Supply Temperature

...

  • #23,#24: CCITT KERMIT checksum

NOTES:

One read frame with according readouts from display ~1 minute earlier: frame=210a0a84170011000001ee01af001e0295010080b3001e015a4a

interpretation so far: ebv water_nominal=17.5,burner_temp=54.2,burner_mode=1,outdoor_temp=17.9,supply_temp=28.6

18,0 3:1 Aussentemperatur aktuell OK 16,5 3:2 Aussentemp Langzeit 11,0 3:3 Aussent. min 24h 19,5 3:4 Aussent. max 24h 54.0 4:1 Temp Brenner OK 40.5 4:2 Soll Brenner 0 4:3 Brennerstatus 1093 4:4 Starts Brenner 1259 4:5 Betriebsstunden Brenner 1 6:1 Anzeige Heiskreispumpe 28.5 6:4 Vorlauf Heizkreis soll OK 20.5 6:6 Raum Solltemperatur 0 7:1 Anzeige Warmwasser Ladepumpe

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