Ah, sorry, .. It's a IXY900IS - running the "ixus850_sd800-100e-0.9.9-890-full"
Pressing "display" turns off display, then it can be pressed and less information appears.
with CHDK , "display" switched off display, and it can wake up only by selecting another photo mode (rotary selector) - but the preview won't come back, and camera cannot even leave the ALT mode, (printing button stops working)
So I hoped for script commands - or settings..