Some ASCB users (ex: FMCS, EDAU) use a number of multiplexed transmission to broadcast all of their current data. The “data header” bits of specific ASCB messages specify the current alternate data index. On any MX Foundation user channel, it is possible to enables the alternate data for each bus side (left/right) independently. When enabled, bits 12-13 of the first data word will be set automatically by MX Foundation for each alternate data. In this case, each alternate data has an associated message queue. To update the user data, write to the buffer associated with alternate by mxfASCBUserBusEnableSet().