ST-980Plus / TME and TDR Return AB Settings optionsSettings | Radio Menu Settings
TMR - This mode select what displays are monitored in the background in addition to the primary (main) selected channels. You can mix and match between all or some of the channels for dual, tri or quad watch.
The options in the programmer include M+A, M+B. / M+A+B, M+C+D/ M+A+B+C, etc to allow you to monitor other channels while working a "M" main channel.
TDR Return AB is a rename for clarity of TMR-MR option. This option is a transmit delay return time that is the delay time before returning to the primary channel after the secondary signal drops. (In other words... the time before you can transmit after listening to a signal on another channel of the display.)