Boundary Scan Test Interface
14.5.7IDCODE (1110)
The IDCODE instruction connects the device identification register (or ID register) between TDI and TDO. The ID register is a 32-bit register that allows the manufacturer, part number and version of a component to be determined through the TAP.
When the instruction register is loaded with the IDCODE instruction, all the boundary-scan cells are placed in their normal (system) mode of operation.
In the CAPTURE-DR state, the device identification code (specified at the end of this section) is captured by the ID register. In the SHIFT-DR state, the previously captured device identification code is shifted out of the ID register via the TDO pin, whilst data is shifted in via the TDI pin into the ID register. In the UPDATE-DR state, the 1D register is unaffected.
14.5.8 BYPASS (1111)
The BYPASS instruction connects a 1 bit shift register (the BYPASS register) between TDI and TDO.
When the BYPASS instruction is loaded into the instruction register, all the boundary-scan cells are placed in their normal (system) mode of operation. This instruction has no effect on the system pins.
In the CAPTURE-DR state, a logic 0 is captured by the bypass register. In the SHIFT-DR state, test data is shifted into the bypass register via TDI and out via TDO after a delay of one TCK cycle. Note that the first bit shifted out will be a zero. The bypass register is not affected in the UPDATE-DR state.