UART simulation in ModelSim

Hi,

I'm trying to simulate my design that is based on NIOS2 with UART. ModelSim is the simulating program. For this purpose I wrote a small C program for NIOS that knows to send sequence of chars and receive them. In my TestBench I put loopback between input and output of UART. In simulation wave windows I see the chars are being transmitted and entering into Rx shift register but after that they are not recognised by UART and are not taken into internal register.

Have anyone any ideas?