Dual-purpose shift register

A fuse programming circuit for sequentially programming a plurality of fuses, comprising:

• a shift register having:
• a data input;
• a plurality of stages, each comprising a fuse latch circuits for holding fuse programming data indicating which of the fuses are to be blown, and a pointer latch circuit for holding bits of a pointer for selecting one of the fuses;
• transfer circuitry for serially transferring bits of data presented at the data input and to be stored in the fuse latch circuits through the plurality of stages during a first mode of operation;
• and
• a pointer advance circuitry for serially advancing the pointer to select different fuses without disturbing bits of data stored in the fuse latch circuits in a second mode;
• and
• one or more blow circuits configured to apply a blow voltage to a fuse selected by the pointer if the fuse programming data stored in a corresponding fuse latch circuit indicates the selected fuse is to be blown.

A method for maintaining both pointer and data information in a shift register having multiple stages, each stage having a pointer latch circuit and a fuse latch circuit, the method comprising:

• shifting data bits into the data latch circuits through the pointer latch circuits;
• decoupling the data latch circuits and pointer latch circuits;
• initializing a pointer formed by bits stored in the pointer latch circuits to select a first stage of the shift register;
• and
• serially advancing the pointer to select a second stage of the shift register by changing one or more bits stored in the pointer latch circuits without disturbing the data bits in the data latch circuits.

A method for sequentially programming a plurality of fuses, comprising:

• (a) loading a shift register having a plurality of stages with fuse programming data, wherein each stage of the shift register comprises a pointer latch circuit and a data latch circuit and each data latch circuit is configured to store a bit of fuse programming data to indicate whether an associated one of the fuses is to be blown, and wherein loading the shift register comprises serially transferring bits of fuse programming data present at a data input and to be stored in the data latch circuits through the plurality of stages;
• (b) initializing a fuse pointer, formed by bits stored in the pointer latch circuits, to select a fuse;
• (c) blowing the fuse selected by the fuse pointer if the bit of fuse programming data stored in the associated data latch circuit indicates the fuse is to be blown;
• (d) advancing the pointer to select a subsequent fuse;
• and
• (e) repeating steps (c)–(d) until each of the fuses to be blown, as indicated by the respective bit of the fuse programming data, have been blown.

A shift register circuit, comprising:

• a data input;
• a plurality of stages, each comprising a data latch circuit for storing a bit of data;
• a pointer latch circuit for storing a bit of pointer information;
• transfer circuitry for serially transferring bits of data presented at the data input and to be stored in the data latch circuits through the pointer latch circuits and data latch circuits of the plurality of stages during a first mode of operation;
• and
• pointer advance circuitry for serially transferring one or more bits of pointer information forming a pointer through the plurality of stages during a second mode of operation without disturbing bits of data stored in the data latch circuits.