Units are needed to follow a protocol so which the interrupt-ask for (IRQ) traces is often shared. The PCI bus includes four interrupt lines, INTA# by INTD#, all of which can be found to every gadget. Up to eight PCI products share the same IRQ line (INTINA# by INTINH#) in https://nathanlabsadvisory.com/navigating-cybersecurity-and-risk-management/