problem about simulating altiobuf

I am using an ALTIOBUF megafunction in my design. it works as a LVDS tx buf.

Its outputs(dataout and dataout_b) stay at z when being simulated.

in the generated file(lvds_tx_buf.v) devoe of cyclone_iii_obuf is connected to 0.

---------------------------------------------

cycloneiii_io_obuf obufa_0

(

.i(wire_obufa_i[0:0]),

.o(wire_obufa_o[0:0]),

.obar(wire_obufa_obar[0:0])

`ifdef FORMAL_VERIFICATION

`else

// synopsys translate_off

`endif

,

.oe(1'b1),

.seriesterminationcontrol({16{1'b0}})

`ifdef FORMAL_VERIFICATION

`else

// synopsys translate_on

`endif

// synopsys translate_off

,

.devoe(1'b0)

// synopsys translate_on

);

defparam

obufa_0.bus_hold = "false",

obufa_0.open_drain_output = "false",

obufa_0.lpm_type = "cycloneiii_io_obuf";

---------------------------------------------

In module cycloneiii_io_obuf in cycloneiii_atoms.v

---------------------------------------------

assign tmp1 = (devoe == 1'b1) ? tmp : 1'bz;

assign tmp1_bar = (devoe == 1'b1) ? tmp_bar : 1'bz;

pmos (o, tmp1, 'b0);

pmos (obar, tmp1_bar, 'b0);

---------------------------------------------

i don't know if i have explained the problem exactly.

how to solve the problem?