Identification Protocol
Fixed bit patterns embedded within the boundary scan architecture of a semiconductor allow external test equipment to verify the identity of the chip. The jtag idcode is a thirty two bit value that is shifted out of the device when the identification instruction is executed. This value is unique to a specific part number and manufacturer.
Bit Arrangement
Internal fields within the code define the version number, the part number, the manufacturing location and the identity of the company as assigned by the industry association. When a tool reads the jtag idcode, it parses these fields to determine which data register lengths and instruction sets are supported by the chip. This automated detection simplifies the configuration of the test environment.
Verification Flow
Production systems use the code to ensure that the correct component has been soldered onto the board before starting the functional test. If the jtag idcode does not match the expected value in the database, the test software halts to prevent damage to the hardware or the recording of false data. This check is often the very first step in a boundary scan test sequence.
Tool Interaction
Debugging software relies on this identifier to load the correct description files for the internal architecture of the processor. Without this code, the debugger would have no way to know how to interact with the silicon.
