Selecting on die test port and off die interface leads
An IC includes an IEEE 1149.1 standard test access port (TAP) interface and an additional Off-Chip TAP interface. The Off-Chip TAP interface connects to the TAP of another IC. The Off Chip TAP interface can be selected by a TAP Linking Module on the IC.
1. A process of operating an integrated circuit die, comprising:
A. shifting onto the die instruction data into an instruction register in response to TDI, TCK and TMS signals received, respectively, on a TDI input lead, a TCK input lead, and a TMS input lead from off the die; and
B. selecting on the die one of a test access port, which includes a controller connected to the TCK lead and the TMS lead, and an instruction register and a data register connected to the TDI input lead and to a TDO output lead and the data register being coupled to functional circuitry, and an off die interface, which includes a TDI output lead, a TCK output lead, a TMS output lead, and a TDO input lead.
2. The process of claim 1 including selectively coupling the TDI output lead to the TDI input lead, the TCK output lead to the TCK input lead, the TDI output lead to the TDI input lead, and the TDO input lead to the TDO output lead.