The TCK (pin 2), TDI (pin 3), TDO (pin 4), and TRST (pin 139) pins are JTAG pins, and are generally used for in-circuit testing, also known as bed of nails or boundary scan testing.
- TCK: test clock
- TDI: test data in
- TDO: test data out
- TRST: test reset
You would generally perform this testing on your board after it was built to test the TNT5002.
These pins must be wired out of the board in order to do JTAG testing. They can also be routed into a single scan chain.
If you are not doing JTAG testing, the pins are not used in normal operation, and should generally be left unwired.
For more information regarding JTAG, please refer to the links below.