///////////////////////////////////////////////////////////////////////
//
// switch module
//
//
///////////////////////////////////////////////////////////////////////

`ifdef switch_access_time
  // already defined - do nothing
`else
  `define switch_access_time 500ns
`endif


module io_switches ( switches, Data, nOE, nCE, nWait );

output nWait;
input [15:0] switches;
inout [15:0] Data;
input nOE, nCE;

specify
  specparam tViolate=250;
  $width(negedge nCE, tViolate);
  $width(posedge nCE, tViolate);
  $setuphold(edge[10, 01] nCE, nOE, tViolate, tViolate);
endspecify

reg delay;

initial
  delay = 0;

always @(negedge nCE)
  begin
    delay = 1;
    #`switch_access_time
    delay = 0;
  end 

assign nWait = (delay && !nCE && !nOE) ? 0 : 1'bz;

assign Data = ((nOE == 0) && (nCE == 0) && (delay == 0)) ?
                    switches : 16'bz;

endmodule