The DX28 has two optically-isolated NMEA 0183 inputs which each drive four NMEA 0183(RS-422) outputs. Normally, the two channels (PRIMARY & AUXILIARY) are completely independent of each other and can therefore operate at different baud rates. In “Autoswitch” mode, however, a loss of PRIMARY data for 5 seconds automatically switches all 8 outputs to the AUXILIARY input. When the PRIMARY signal returns, the DX28 immediately switches all 8 outputs back to the PRIMARY input. Each bicolor LED shows which channel it is sending, Green for PRIMARY, Red for AUXILIARY. Autoswitch mode is enabled by connecting the "Auto" terminal to "GND". For a single input 8-way Expander, the two inputs can be strapped together, or the unit can be left in "Autoswitch" mode with the input signal connected to PRIMARY.

The outputs are separately driven so that shorting one output does not affect the others. The output drivers employ a standby state whereby they are disabled until an input signal appears, causing immediate enabling of the outputs. This results in very low power consumption and high immunity to shorted outputs. Each output is also individually lightning and surge protected.

The DX28 uses a very efficient DC power converter allowing it to operate from 10-30 Vdc with less current draw in standby state than an indicator LED uses. For that reason a power LED indicator was left off the design.