How to copy SBUF in SPIDAT

Hi everybody !

I'm currently working on a project with a ADuC847 and I would like to copy the content of SBUF (data register of UART) to SPIDAT (data register of SPI).
Here is a part of my code:

T3CON = 0x83; //9600 Baud rate

T3FD = 0x12;

SCON = 0x52; // UART enable, variable baud rate.

SPICON = 0x2C; // SPI enable, slave mode

while(!RI); //interrupt flag of UART (Set when SBUF is full)

if(ISPI==0 && RI==1)

{ SPIDAT = SBUF; // This line doesn't work. Value is still egual to 0

value = SPIDAT; }

RI = 0; ISPI = 0;

Someone would have any idea ?
thanks in advance,

Guillaume.