Addressing Port 5 on a 80C552?

I want to use a single Port line from P5 as an input! Are there special settings for this port (e.g. setting a bit in a register;...)? Exsist some special configuration in µVision?

The standrad way I tryed was:

sfr     P5		= 0xC4;     
sbit	SI1		= P5^7;

I get the error "Incalid base address"!
I know, this is a simple and maybe stupid error.

I would be very pleased, if somebody could answer this problem

Thank you
Christian