Looking from the back of the HD80, the power switch is on the far left (once for on, twice for off). Next is the Menu button, followed by the up and down arrows, then the left and right, and finally, the Enter key. The left arrow doubles as the Source select button when the menus aren't in use, and the right arrow, doubles as the re-sync button, primarily for locking on to a PC analog source.
Moving to the back, the input panel is especially well endowed. I say this because the HD80 has three digital inputs; two HDMI inputs and a DVI. The DVI, can be used for a digital input, or as either a second component video, or as the analog input for a computer. The dedicated component video input has the usual three RCA jacks. To round things out, there's the traditional composite, and S-video inputs, an RS-232 for "command and control" by a room control system or computer, and a 12 volt "trigger" for controlling a properly equipped motorized screen.
As a typical DLP projector, the HD80 has a sealed light path, and no filters to change out