To do this, I purchased a B&B Electronics Model 232CL4R converter. To hook it up to the Mod8 is relatively easy. The TTY Out signals go to the R+ and R- terminals, and the TTY In signal goes to the T+ and T- terminals on the converter. No external power supply is needed (despite what is shown in the diagram below). I discovered this by accident when I ran the system without plugging in the current loop RS232 cct power supply..