BLVDS in Cyclone IV E

Hello,

i did not find some good note how to implement bi-dir BUS LVDS on Cyclone IV E. My current settings still returns error.

I have one differential signal on fpga which should be used as blvds to half duplex communication between a few cards. There is a note in the manual BLVDS can be used as bidirectional bus to half-duplex communication. The second note which I found says that differential signals have open-drain option disabled. It does not make sense to me. How can I enable open-drain for BLVDS? Because when I use bi-dir blvds quartus returns this error message:

Error (169008): Can't turn on open-drain option for differential I/O pin fe_reset_n_p

When I use ALTIOBUFF and when differential mode is selected then open-drain cannot be used.

Can Cyclone IV E use bi-dir blvds for half-duplex communication?

Thank you for help,

vkle