i2c from altera wiki

Thank FvM for your reply.

I check the signal connections from bottom module to the top module.

I think the scl_o and sda_o signals in i2c_master_bit_ctrl module are actually the signals scl_pad_o and sda_pad_o in the top module "opencores_i2c".

If the scl_padoen_o and sda_padoen_o are low, scl_pad_o and sda_pad_o are selected as the external output signals.

So this is why I check scl_o and sda_o in my simulation.

assign scl_pad_io = scl_padoen_o ? 1'bZ : scl_pad_o;
assign sda_pad_io = sda_padoen_o ? 1'bZ : sda_pad_o;