#1. "RE: SB-20 & Vivitar 283 slave use" In response to Reply # 0
1. Multi-sensor balanced fill flash, except in manual exposure mode or with spot meter, which will be standard TTL. (p.86, N80 manual)
2. You can use just about any flash as the slave. All you need is a slave trigger. Typically, the camera is in Aperture Priority, and the on-camera flash is set to TTL. The slave is positioned so that it is not pointing directly at the camera. It is usually set to Manual, with the distance and/or power that will give a one-stop underexposure. For example, camera set to f5.6, and the slave flash situated in such a way that it would require f4 for the correct exposure. This provides a nice lighting ratio, and is also recommended to keep the TTL flash from shutting down to soon, thus causing underexposure overall.
3. The one and only off-camera TTL cord is the Nikon SC-17. The chart in the manual is a little hard to interpret here, but I think this will give you standard TTL only.