 Unlike the 8563, the 8568 included an unused (in the C-128) active low interrupt request line (/INTR), which was asserted when the "ready" bit in the 8568's status register changed from 0 to 1.Reading the control register would automatically deassert /INTR.Owing to differences in pin assignments and circuit interfacing, the 8563 and 8568 are not electrically interchangeable.