Andy Neil said


Not really new to the 8051 I have been studying the data sheets etc and bought some software to compile and debug 8051ASM actually this is an old system that uses a 80C31 a romless 8051 of course
I have plenty of practice using atmel AVR asm so assembler is not relatively new to me I prefer to write in assembler over C



MOV SCON, #13h
only command in whole program that refers to SCON
Loading SCON with #13H is equivalent to enabling both TI, RI and REN enabling reception, also this means that the serial port is in mode 0
unless I am misunderstanding the data sheet I think I am correct

I myself was pretty sure that it was a "loopback" as some people have mentioned what goes in comes out the reason I wanted to confirm this was because I am sure that no data that comes in from the serial port actually makes it to external RAM that is what I wanted to confirm?, which makes the rest easy for me this also links to my other post of moving asm to c which is not needed if this is the case.
unless there is some other trick way of getting data into the external RAM knowing that the only one routine/command in the whole asm code that refers to SBUF iS the previously mentioned command

MOV SBUF,SBUF

I assume if any data made it to external RAM then the code would have had to MOV the DPTR to some external ram location then move the SBUF data in