Changes the current TAP instruction.

4 bits.

In the SHIFT-IR state, the instruction register is selected as the serial path between TDI and TDO.

During the UPDATE-IR state, the value in the instruction register becomes the current instruction.

During the CAPTURE-IR state, the binary value 0001 is loaded into this register. This value is shifted out during SHIFT-IR. On reset, IDCODE becomes the current instruction.

The least significant bit of the register is scanned in or out first.