bidirectional pin simulation for serial I2C

For me it is strange, that you perform read and write to SDIO at the same time. I was using bidirectional pins. VHDL description looks like this:

IO <= output when OE = '1' else (others => 'Z');

Controlling the OE signal you can change the direction of IO pin/bus. As for simulation, you can observe data out , but reading from IO is practically impossible.