Sorry pin12 is not mapped in the software. however you can use other pins on J10, eg 6,7,8, and 9. These are already mapped to HiCON port 14 pins 4,2,0, and 6.
Use a simple switch or an open collector / open drain type output to drive these pins to ground / 0v. They are pulled up inside the unit to 3.3v, so your external output will just pull it down. To verify your output is safe for integra, take a 4.7K 1/4w resister, tie one end to the output, and the other end of the resister to 3.3volts on J6 (2nd pin from Ethernet port, label is wrong on it, should say 3.3v). turn on the output, it should read 0 volts. turn off the output, it should read 3.3volts.
regards.
Rufi