Using the IGC (backwards) RJ45 numbering scheme:

IGC standard RJ45:
1,2 +12V
3
4
5 RS232 TX
6 RS232 RX
7,8 GND

LXNAV v7 RJ45 PDA port:
1,2 GND
3 RS232 TX
4 RS232 RX
5 TTL TX
6 TTL RX
7,8 +5V

Hopefully I've messed up transcribing those. If not, it's certainly an
interesting
design choice.