MIL-STD-1553B is a 1 Mb/s command/response, dual-redundant, time-multiplexed serial data bus used in aircraft, spacecraft, military vehicles, and severe control environments. Core1553BRT provides a complete, MIL-STD-1553B Remote Terminal (RT), and is compatible with legacy remote terminal systems and supports standard off-chip 1553B transceivers. Core1553BRT_APB supports all 1553B mode codes and allows the user to designate as illegal any mode code or any particular subaddress for both transmit and receive operations. The command legalization can be completed within the core or using an external command legality block via the command legalization interface.