Changes

Hi. This method to reduce scroll speed is not really "smooth" because register 3 does not give a step with exactly one byte length. The only way to reduce scroll speed and keep a smooth effect is to use two videos data areas (offset switching). The inconvenient of switching is to need more memory (2x). By the way, it's the right way and the only method known on cpc old to code a slower hardware scroll (1/2 byte : 2 pixel mode 1, 1/4 byte : 1 pixel mode 1)

Great article on Interrupt Im0 on Cpc+...