How to unlock a decoder

CV15 is the “KEY”. This CV is always programmable even when “locked”

CV16 is the "LOCK"  

When CV15=CV16 the decoder is unlocked and will respond to programming commands.

If CV15 is not equal to CV16 then decoder programming is locked and it will not program (except CV15) or read.

The Factory Defaults for both CV15 and CV16 is 0