Hi Krasimir,

please check the generated code,
for "mov A,P4" it must be: E5 D8

Otherwise its a syntax error or a compiler error, but on the Keil compiler it works.
Maybe some controls missing, since on the Keil it must be written:

#pragma src
#include<reg51.h>
sfr P4=0xD8;

#pragma asm // switch from C to inline assembler
mov a, P4
mov SBUF, a
#pragma endasm // switch back to C


Peter