Address Name Description
DFF1EC BPLHPTH UHRES (VRAM) bit plane pointer (high 5 bits)
DFF1EE BPLHPTL UHRES (VRAM) bit plane pointer (low 15 bits)


When UHRES is enabled, this pointer comes out on the 2nd 'free' cycle
after the start of each horizontal line. It‘s modulo is added every
time it comes out. ’free' means priority above the copper and below
the fixed stuff (audio,sprites….).
BPLHDAT comes out as an identifier on the RGA lines when the pointer
address is valid so that external detectors can use this to do the
special cycle for the VRAMs, The SPRHDAT gets the first and third
free cycles.

This material is most likely derived from the official Amiga documentation and where applicable copyright remains with the original author.