On 2013-05-17 16:32, Bob Armstrong wrote: I thought the DELQA did? I don't think the DEQNA did, however. Also, the DEUNA and DELUA handles it, as far as I know. I thought I remembered that the Ethernet interfaces could do it, but how does that work? The DMR required that you have a M9312 with the appropriate boot ROMs - were there NI boot ROMS for the M9312 too? How did the DELQA do it (i.e. which QBUS PDP-11 CPU had an NI boot ROM)? Actually, this is a bit more complex, as well as me not being 100% sure about all the details. But essentially, yes, there are boot ROMs for the DEUNA/DELUA, but they are not involved when you do a trigger command. As for the Qbus machines, the 11/73/83/93 all can boot from ethernet with the standard boot roms, unless I remember wrong (you just need the right revision). However, I believe that these too are not used when you do a MOP trigger. As far as I remember (I seem to remember this being documented in the DEUNA and DELUA manuals), at a MOP trigger command, the ethernet card resets the bus, and then it forces the CPU to jump into boot code provided by the ethernet controller. This is done by forcing a different restart vector for the CPU. And yes, the controller have PDP-11 code in ROM, for booting. It just makes this code appear in the I/O page for the CPU to execute, at trigger time. The boot ROM is needed when you want to network boot from scratch, as there is no MOP trigger to activate the ethernet controller in that case. It's actually three ROMs for the M9312 to implement the NI booting. But for just the trigger boot, those ROMs are not used, or needed. Also, the DMR was smart enough to implement DDCMP in "hardware" and so it understood MOP at least well enough to detect the TRIGGER message. The DEUNA/DELUA/DEQNA/DELQA has no reason to implement DDCMP, although it certainly had enough local CPU power to do so. Did it still scan for MOP trigger messages anyway? Or was the Ethernet trigger implemented differently? Of course. DDCMP has nothing to do with this. MOP is defined over Ethernet as well. And yes, the controllers understand and handle some MOP packets internally in the controllers, if needed. Johnny