in HT12E chip the 4 bit digital code with 8 bit address transmitted serially by means of specially designed protocol.
HT12D receives these 12 bits extracts 4 bit digital code. so in this case you need not to develop your protocol. its built in enc-dec chips
if you want to transmit serial data through UART wirelessly, you need to develop such protocol. simple UART with MAX232 is not at all a wireless protocol. i think now it will be clear to you.