Products are required to comply with a protocol so the interrupt-ask for (IRQ) traces could be shared. The PCI bus contains 4 interrupt traces, INTA# via INTD#, all of which are available to each unit. As much as 8 PCI equipment share the same IRQ line (INTINA# through INTINH#) in https://nathanlabsadvisory.com/nerc-cip/