YUN rev 2 softwareSerial, bridge, I2C, RS485

[jordy_m]

Hi,
as you can see on the attached pic, I have a board that the YUN is siting on.
D2 and D3 are used for I2C comm.
D0 and D1 were suppose to be used for the RS485 comm.
later I found out that D0 and D1 are used for the bridge (I received wrong information from the slaves).
my problem is that most of the pins are already in use.
The only pins that available are D12 and D13 ( I don't use the DAC for now) without any new editing of the board.

1. what pins can be use as RX?
2. what pins can be use as TX?
3. I tried to use D13 as RX and D12 as Tx using SoftwareSerial but I can't see any data sequence. only the switching of the pin.
   
   

any suggestions?