9.6. IEEE Std. 1149.1 Boundary-Scan Register
The boundary-scan register is a large serial shift register that uses the TDI pin as an input and the TDO pin as an output. The boundary-scan register consists of 3-bit peripheral elements that are associated with Intel® Arria® 10 I/O pins. You can use the boundary-scan register to test external pin connections or to capture internal data.