BLENDSCREEN bmp$ [, duration%]
Fades the current back buffer (hidden surface) into the picture bmp$. Like a smooth version of LOADBMP.
The duration% offers a possibility to control the duration of the blending in milliseconds. If it's left, 1000 ms is assumed.
PRINT "Back-Buffer previous", 100, 100
Note : On the iPhone, this command only works in Portrait mode.