Every rotation of a motor causes a switch to be pushed. The switch, like most mechanical switches, 'clatters' or bounces when the contacts come together, causing an interval when a single press causes...

Extracted text: Every rotation of a motor causes a switch to be pushed. The switch, like most mechanical switches, 'clatters' or bounces when the contacts come together, causing an interval when a single press causes multiple closures. This bouncing can continue for just under 3 milliseconds. The switch is linked into the memory map of a 68000 processor at bit 0 of location $FFFFF000. It is connected so that the bit will read a '1' when the switch is open, and a '0' when closed and not bouncing. The bouncing will cause alternating zeros and ones. For ease of any analysis you do, assume that every instruction takes 1 usec., regardless of addressing mode.