"115200 baud " With a 8052 core ? Possible ?
absolutely. Take e.g. a 33MHz 12 clocker and calculate the ISR time. OIf course if you are not a believer in KISS as far as ISRs go, it is impossible.

ISR
xmit
Mov a,@Ri
mov SBUF,a
inc Ri
reti

MAIN
IF RI=END
ES = 0

and similar for receive

Erik

PS KISS = Keep It Simple, Stupid