SoundTraxx Tsunami Steam Users Guide - Manual (Page 17)

Tsunami Steam Sound User’s Guide Page 14
Once the extended address is stored in CV 17 and 18, bit 5 of CV 29 must
be set to 1 so the decoder will recognize the extended address format.
Otherwise, the decoder will continue to respond only to its primary address.
See the next section, Configuring the Decoder.
Basic Programming