I'm restoring a pdp11/34a, and I've got a weird problem I'm hoping someone out there can help me with. The system seems to be working just fine, with one exception: bus reset just doesn't work. The unibus is configured correctly; I've verified that NPR is jumpered/granted correctly through the bus. This is a BA11-L box with the DD11-PK 9-slot backplane, configured like this: Slot 1 - CPU Slot 2 - CPU Slot 3 - A/B M9312 bootstrap/terminator, C/D/E/F M7859 front panel programmers interface controller Slot 4 - 128 Kword MOS memory Slot 5 - RL11 controller Slot 6 - C/D/E/F M7856 DL11-W console RS232 interface Slot 7 - C/D G7273 dual bus grant Slot 8 - C/D G7273 dual bus grant Slot 9 - A/B M9302 terminator, C/D/E/F M7856 DL11-W configured at 776500 for TU58 tape drive The symptoms: At poweron, the system starts the M9312 console emulator software; I can use it to deposit a small program into memory with no problem. Attempting to use the "S" command to actually start the program causes the RUN light to come on; the program never executes, hitting CTRL/HALT on the front panel causes BUS ERR, the RUN light stays on, and the only way to regain control of the system is power off. For example: @ L 1000 @ D 000777 @ L 1000 @ S fails as described above. If I use the front panel to install a program and run it, when I push CTRL/START, the system halts at the start address. For example: CTRL/HALT CLR 1000 LAD CLR 777 DEP CLR 1000 LAD CTRL/START the system halts, run light out, at address 1000. If I then press CTRL/CONT, the RUN and SR DISP lights come on, and everything works perfectly. I can CTRL/HALT the system, continue, etc. With no problem. Furthermore, if the program I enter contains a RESET instruction (000005), the behavior of the system as it executes that instruction is pretty much exactly like using the "S" command from the console emulator - RUN stays on, CTRL/HALT causes BUS ERR, and the system is non-responsive until I power the beast off. For example: CTRL/HALT CLR 1000 LAD CLR 240 DEP DEP DEP CLR 5 DEP CLR 1000 LAD CTRL/START (the system halts at address 1000) CTRL/HALT (single steps to location 1002 correctly) CTRL/HALT (single steps to location 1004 correctly) CTRL/HALT (single steps to location 1006 correctly) CTRL/HALT (RUN light comes on, CTRL/HALT causes BUS ERR with RUN, system is no longer responsive, have to poweroff) My reading of the unibus tech manuals indicates that there is no ACK of any kind for BUS INIT, so I am somewhat confused. There _is_ a bit of noise on the +5V power supply; a voltmeter shows 5.02 volts stable, but there is a .5V spike at 50 kHz showing on the scope; I can't see this causing problems _only_ with BUS RESET. I have also verified that CTRL/INIT from the front panel seems to do nothing at all. For example, if I halt the system and press a key on the console emulator, examining 777560 shows 000200 (which is correct, there is a character available at 777562). Pressing CTRL/INIT on the front panel does _not_ clear 777560 - it still shows 000200. All the 11/34a M9312 diagnostics run fine. This problem seems to be limited to attempts at RESET. A disassembly of the M9312 console emulator code shows that two things happen when you use the "S" command: 000005 (RESET) followed by a JMP (R5) It's the RESET that drives the machine nuts. Anyone have an idea? -- <http://www.liveblockauctions.com> Roe Peterson / Director of Research & Development O. 306.523.4005 / C. 306.501.6802 *Help Desk: 1.877.694.6100 / 306.694.6100* <http://www.liveblockauctions.com/index.php?p=FAQs>