VLSI chip having improved test access

Claim 1

An integrated circuit comprising: input shift chain means comprising a plurality of input means arranged in an ordered linear array including a first input means, one or more intermediate input means, and a last input means, each said input means comprising external connection means, memory means, and multiplexer means, said external connection means including means for receiving an external signal specifying one bit of information, said memory means comprising means for storing one bit of information specified by an input signal on a memory input thereto, said bit of information being stored in response to a clock signal, and signal generating means for generating a signal indicative of said bit of information currently stored in said memory means; and said multiplexer means comprising first and second inputs, a control input, and a multiplexer output, said first input being connected to said external connection means, said second input being connected to said generating means in the memory means prior to said memory means in said ordered linear array, and said multiplexer output being connected to said memory input, said multiplexing means connecting said first input to said multiplexer output if a first control signal is present on said control input and said multiplexer means connecting said second input to said multiplexer output if a second control signal is present on said control input; said integrated circuit further comprising: scan register means comprising a shift register, the shifting operations thereof being responsive to said clock signal; means for connecting said signal generating means of said last input means to the input of said shift register; and control means responsive to one or more external control signals for generating said first and second control signals without altering the contents of said scan register and coupling said first and second signals to each said multiplexer means.