Circuit for designating an operating mode of a semiconductor memory device

摘要

A circuit for designating an operating mode of a packaged semiconductor memory device includes a first fuse mounted on the device. A plurality of pads mounted on the device are accessible to a user after the device is packaged. A mode selection circuit generates a first signal when the first fuse is open and a second signal when the first fuse is closed. A first-fuse opening circuit is operably connected to the pads and opens the first fuse responsive to a predetermined first-fuse cutting signal on the pads. In another aspect of the invention, a second fuse may be opened responsive to a predetermined second-fuse cutting signal on the pads. When the second fuse opens, the first-fuse opening circuit is disabled to prevent accidental opening of the first fuse when the desired operating mode requires the first fuse to be maintained intact.