Richard / Ian,
With the exception of the GPS input (NMEA 0183) and Baud rate (both must be set to the same rate, but 9,600 as quoted by Ian previously should be fine), none of the other settings on the TT21 should be critical to getting it to transmit (though some of course would lead to 'illegal' transmissions).
The PAW settings are simply 'Transponder Trig' and the Baud Rate for the correct USB port.
Having assisted with setting up several of these units for ADSB Out via PAW, The two most common issues I have come across are...
1. Setting up the wrong USB port in PAW. The numbering is NOT as shown on the Quick Start Guide. Lookin at the PAW with the Ethernet port to the left, the USB ports are numbered:
Ethernet 1 3
Port. 2 4
2. Misreading the pin numbering in the 25 pin connector - remember the pins are numbered from the top right looking at the BACK i.e. CABLE SIDE of the plug, NOT the connecting face.
If both of these are definitely correct Ian, I am frankly stumped.
If you still can't get it working after rechecking your wiring, let me know and I will pop down to Trig and have a chat with the technicians for you.
Regards
Peter