How to read the 9th bit from S1OUT?

I can write 9 bits to S1IN, like:
S1IN = 0x130;
...

But I can't read 9 bits from S1OUT. I have done the following:

FUNC void myfunc(void){
unsigned int bytein;
bytein = S1OUT;
printf("%x\n",bytein);
...
if(bytein>>8){ ... }
}

but it never work. Any suggestion?