Default fuse condition for memory device after final test

A test system for a serial EEPROM device, said device including a memory array;

• programmable option means for selectively configuring at least a portion of the memory array to possess a programmed characteristic selected from the group consisting of write protection, endurance, organization, density and protocol;
• configuration fuse means having two programmable states including one state for preventing alteration of the characteristic after programming thereof and another state for allowing the characteristic to be reprogrammed;
• and lockout fuse means having two programmable states including one state for rendering the configuration fuse means programmable only once thereafter and another state for allowing the configuration fuse means to be programmed repeatedly to either of its two states;
• said test system comprising test means for overriding the lockout fuse means to permit testing of the configuration fuse means and thereafter bring the lockout fuse means and the configuration fuse means to a default condition in which the lockout fuse means assumes its said one state to restrict the configuration fuse means to one-time programming thereafter.

A method of providing programmability of any of a multiplicity of configurable options selected from among write protection, endurance, density, organization and protocol of an EEPROM device so as to permit that programming capability to be verified during factory final testing while securing the device against loss of the programming capability as a result of such testing, and to assure that the device is usable and one-time programmable by the manufacturer's customer after shipment of the device from the factory, including the steps of:

• rendering each of the configurable options of the EEPROM device programmable to allow said customer to select a desired available configuration of any of said options,
• reversibly fusing the programmability of the configurable options to selectively prevent or allow further programming of the configurable options to enable repeated reprogramming for factory testing purposes,
• further fusing the reversible fusing of configurable options programmability to lock out any further programmability of configurable options once set by said customer, and
• during factory final test, overriding the further fusing to allow the repeated reprogramming of the device and upon completion of the testing placing the fusing in a default condition in which the reversible fusing is restricted to one-time programmability of configurable options thereafter.