Velbus Protocols

I have regarding VMB4RY Protocol - edition 1 (available for download in 4 CHANNEL RELAY MODULE page info ) .

When I compare these specification with your demo project I see that High priority and Low priority bytes have different values in both references.

Demo: High: 0xF8 Low: 0xFB
Protocol document: High: 0x00 Low: 0x11

This make me some confusion, likewise STX and ETX bytes.
If possible I would like that you explains me how it’s works.


The high and low priority values are the bit 0 and 1 of a complete byte.
Bit 2 is the start of frame bit (always low) of the same byte and all the other bits (3…7) are high.
The STX and ETX bytes are used to identify the start and end of a messages packet on the pc.

Sorry but I don’t have sure I understand. If it’s possible give me some samples?


STX - start of transfer
ETX - end of transfer

low prority - 0xFB
high priority - 0xF8


FB = 11111011
F8 = 11111000