How to identify the DHP Dual Homing Protocol address in the MiCOM relays?

The DHP is the proprietary redundancy protocol which requires unique addressing for every device connected to the network. This addressing is done thanks to the dip switches in the ethernet boards.
In the last four octets of the ethernet frame some DHP information are available in the following order.

1. bytes n and n-1 are the DHP frame indicators and are always "41 52"
2. byte n-2 is the counter of the DHP frames emitted by the specific IED, it is just hexa to be converted to decimal
3. byte n-3 is the DHP address for the specific IED

• if it is smaller than 128 (80h) it indicates device with the firmware 1.x range (Px3 or Px4 relays), to get the DHP address convert the hexa value to the decimal directly
• if it is bigger than 128 (80h) it indicates device with the firmware 2.x range (Hx6 switches or boards), to get the DHP address convert the hexa value to the decimal and subtract "128"

For example:

• The frames show "d5". After conversion it is 213. It means it is Hx6 switch or board with the firmware 2.x and address 85.
• The frames show "4c". After conversion it is 76. It means it is Px4 relay with the firmware 1.x and address 76.

Released for: Schneider Electric Canada