What is JTAG?

https://www.corelis.com/education/tutorials/jtag-tutorial/what-is-jtag/


One of the key benefits of JTAG is that it provides access to the internal circuitry of a device without the need for additional hardware such as a test probe or emulator. This is possible because JTAG uses a series of test access ports (TAPs) that are built into a device's boundary-scan architecture.


JTAG