11. JTAG Interface Operation
The encoding of the instruction register is given in Table 11-1:
Table 11-1 JTAG Instruction Register Encoding 
The 0001 value is provided to represent sample-preload, but also selects the boundary scan register.
During a reset of the TAP controller, the value 1111 is loaded into the parallel output of the instruction register, thus selecting the bypass register as the default.
During the Shift-IR state of the TAP controller, data is shifted serially into the instruction register from JTDI, and the LSB of the instruction register is shifted out onto JTDO.
During the Update-IR state, the current state of the instruction register is shifted to its parallel output for decoding.
