hi,

serial communication is bit slow....

Well, with standard 8051, UART in mode 2 gives you baudrate = osc/32, i.e. with crystal 11.0592MHz you obtain communication speed 345600 bits per second.

Indeed, SPI provides baudrate as osc/4 max. But if you use the hardware implemented SPI module built-in. If you start to use software-emulated SPI then you lost this speed dramaticaly. Even shortest cycle to send one bit takes 60 clocks:

RLC  A
CLR  SCK
MOV  MOSI,C
SETB SCK

Even more, this time should be increased to give slave device enough time to detect SPI clock, read and send data bit back.

So what I have to say: if you need high-speed communication either use UART (osc/32 max.) or use another derivative with SPI built-in.

Regards,
Oleg