Benutzer-Werkzeuge

Webseiten-Werkzeuge


hardware:vaillantvrt340f_protocol

Unterschiede

Hier werden die Unterschiede zwischen zwei Versionen angezeigt.

Link zu dieser Vergleichsansicht

Beide Seiten der vorigen RevisionVorhergehende Überarbeitung
Letzte ÜberarbeitungBeide Seiten der Revision
hardware:vaillantvrt340f_protocol [2017/05/11 21:23] reinholdhardware:vaillantvrt340f_protocol [2017/05/11 21:26] reinhold
Zeile 150: Zeile 150:
  
 ==== UPDATE: Making sense of the 0xFD byte 13 ==== ==== UPDATE: Making sense of the 0xFD byte 13 ====
-The byte 13 with unknown constant value 0xFD kept bothering me, and a few days after I understood the checksum byte I figured out its meaning too: As I mentioned, bytes 4-12 together with the checksum byte 14 summed up always yielded 0x0300. It seemed strange to me that the 0x03 byte of the sum was somehow ignored, until I realized that 0xFD is actually the binary complement of 0x03, i.e. the checksum is actually just byte 14, but the two-byte value of bytes 13 and 14. So, our assumption that bytes 13 with a value of 0xFD is some kind of End-Of-Data or separator byte was simply wrong, and it being constant is just a coincidence.+The byte 13 with unknown constant value 0xFD kept bothering me, and a few days after I understood the checksum byte I figured out its meaning too: As I mentioned, bytes 4-12 together with the checksum byte 14 summed up always yielded 0x0300. It seemed strange to me that the 0x03 byte of the sum was somehow ignored, until I realized that 0xFD is actually the binary complement of 0x03, i.e. the checksum is actually not just byte 14, but the two-byte value of bytes 13 and 14. So, our assumption that bytes 13 with a value of 0xFD is some kind of End-Of-Data or separator byte was simply wrong, and it being constant is just a coincidence.
  
-In short, bytes 13 and 14 are simply the binary negative of the sum of bytes 4-12, with most significant byte first, i.e. bytes 13+14 interpreted as a signed integer is -sum(byte 4-12). As we are summing up only 9 bytes, there will be no overflow, either (which was what was bothering me with the 0x03 when one understood only byte 14 as the checksum).+In short, bytes 13 and 14 are the binary negative of the sum of bytes 4-12, with most significant byte first, i.e. bytes 13+14 interpreted as a signed integer is -sum(byte 4-12). As we are summing up only 9 bytes, there will be no overflow, either (which was what was bothering me with the 0x03 when one uses only byte 14 as checksum).
  
  
hardware/vaillantvrt340f_protocol.txt · Zuletzt geändert: 2017/05/11 21:28 von reinhold

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki