QUARTUS编译产生如下警告：
Warning (18029): Output pin "_subnet_pin_115" driven by bidirectional pin "sram_bus[10]" cannot be tri-stated.
有以下帮助是这么说的：CAUSE:The specified output pin is driven by both the specified bidirectional pin and tri-stated logic. However, the current device does not support a tri-stated output pin. When the output pin is not driven by either the logic or the bidirectional pin, its output value is undefined.ACTION:If the output pin is always driven by either the logic or the bidirectional pin, no action is required. Otherwise, insert an extra tri-state buffer before the output pin.