Hello All,
To clarify, a “function output” would be a lighting or set of lighting functions in addition to motor control.
Two-function decoders control the motor and typically front and rear lights separately.
Four-function decoders control, not only the front and rear lighting functions separately, but can also add things like interior cab lights, specialized lighting effects like ditch lights, rotary beacons, mars or strobe lights.
Six-function decoders can control- -wait for it- -six separate lighting functions; front and rear lights, interior lights, ditch lights, beacons; rotary, strobe, mars and truck lights, etc.
Sound is not considered a “function” even though you control sounds by “function” buttons on the controller.
As an example, I use 2-function decoders on all my locomotives- -diesel or steam. I only need motor control with separate front and rear lighting capabilities.
On my rotary snowplow I use a 4-function decoder.
This unit is unpowered so it is not self-propelled. The motor function of the decoder controls the motor that turns the fan blades of the plow. I can vary the speed of the blades, through a DCC address, rather than just having it “on or off”.
One function controls the forward headlight. A second function controls the rear-facing light. The third function controls the dual floodlights of the plow (forward) and the fourth function controls a beacon mounted to the top of the cab. This function can be set to “rotary” or “strobe”.
The number of “functions” depends on how many lighting functions you require, not the number of sounds you want.
Hope this helps.