I'm a little confused by the UART I/O memory mapping. If I understand, you edited install.a51 to make BAUDDIV work for you. Did you also change SIOADDR to 0E400H? That would have the UART address range as 0E400H-0E407H, so is it just for the convenience of the decoding that you map it up all the way to 0E7FFH, or is there something more to the mapping that I'm not getting? Do you have the UART's A0-A2 shifted up on the address bus? I'm just trying to establish a better baseline understanding to move forward with assistance.