
I did some basic connection tests with my equipment an gave the pins a number for the identication. Nothing special and not really amazing:
1 - GND
2 - 3.3V (connected to Pin4 of J3)
3
4
5
6
7 - GND
8 - GND
9
10
11 - GND
12 - GND
13 - 3.3V (connected to Pin4 of J3)
14 - GND
So, Pin 3,4,5,6,9,10 remains unknown at the moment (for me!).
Because of less experiance I'm not able to find out where the other pins go to, but there is no direct connection to flash (U5).
Maybe someone is able to compare the B04/B03/P21 to an old v2 Plug with a known JTAG Connector