Assuming that slave is connected to IR1 and slave 2 is connected to IR2 of a master, they are only slaves, and highest priority in all three 8259As is assigned to IR0, the fully nested order of priorities would be: Master: IR0 (highest priority)
Slave1: IR0, IR1, IR2, IR3, IR4, IR5, IR6, IR7
Slave2: IR0, IR1, IR2, IR3, IR4, IR5, IR6, IR7
Master: IR2, IR3, IR4, IR5, IR6, IR7
The masks in the master and slaves may, of course, be used to block out some of the requests.