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Thread: Looking to buy/build a small PDP-11 system

  1. #51
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    Quote Originally Posted by Dare View Post
    So the RUN LED on my make-shift front panel doesn't light when the processor is running. Not a big deal, really. But I am thinking of soldering a jumper on the backplane to connect SRUN/L to the middle row as well.
    The traditional method is wire wrap I had to change over my first QBus chassis, it had been used as an expansion chassis and the RUN lamp would not light as a result.

  2. #52
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    For those who have access to old Cisco Routers (like me ), I found that the power-supply of a Cisco 26xxXM series is quite useful to power-up a small PDP-11, it is rated 7.5A @5V, 1.2A @12V and .5A @-12V and today I discovered that the power-supplys from a Cisco 1841 have even 9.5A @5V. Nice thing is that they are very small, fully enclosed and they have a power-switch and a standard mains plug. They don't need any signal like a AT or ATX powersupply to start.

  3. #53
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    AT doesn't require a power start signal, and ATX you can just tie up the start line or hook it to a switch. As a bonus, with a PC power supply you get a Power OK signal which can be used with the PDP-11.

  4. #54
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    Itˋs more because AT power supplys are hard to find these days or quite expensive (at least where I live) and current ATX are rather weak at 5V and as a bonus the router power supplies are very small. I thought it is aways good to know of alternatives.

  5. #55
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    Quote Originally Posted by cbscpe View Post
    Itˋs more because AT power supplys are hard to find these days or quite expensive (at least where I live) and current ATX are rather weak at 5V and as a bonus the router power supplies are very small. I thought it is aways good to know of alternatives.
    Indeed, knowing of cheap sources for replacement is always good. Didn't mean to sound as if I was putting your discovery down

  6. #56
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    Finally found some time and put everything together. Made a DLV11J serial cable and activated my Christmas present, a UC07 controller. The DLV11J cable was required as I wanted to first boot via TU-58 Emulator. Yesterday I had some strange problems to boot RT-11. XXDP was running but booting RT-11 would hang and stop after loading some parts of the RT-11 image but not enough to even show a small sign of life on the console. I suspected something with interrupts not working and so started again today but first without the UC07 controller. And it worked immediately. Then I added the UC07 and booting RT-11 from TU-58 still worked and it did recognize the MSCP controller and I could even say BOOT DU: to boot the image I had previously copied to the SD-Card. Booting directly from UC07 (via the built-in bootstrap command) works as well. The only thing not working is the line-time clock. That means I will have to do more reverse engineering of the backplane and the Multi-function board. But I'm close to a fully functional system.

    Also I found out the router power supply needs an active cooling and I had to add a (small) FAN, else it would shut-down after about 5 minutes. Now I'm looking for a silent 12cm FAN for the card-cage, the one I currently use is quite noisy. Any suggestions?

    Peter

  7. #57
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    After some more success but also some more failures I learned something very important about my 9-Slot Plessey backplane. BIAKO and BIAKI are not going from Slot 1 to Slot 2 to Slot 3 and so on. Rather BIAKO from Slot 1 (reserved for the CPU) goes to BIAKI to the last Slot 9 (reserved for the Multifunction card that also has the bus terminators) and from there to Slot 2 and then to Slot 3 and so on. Now everything makes sense. SSAPRE2 on Slot 9 goes to the the 50/60Hz source from the power supply. And only Slot 9 receives the clock from the power supply (or whatsover you have, in my case the power-distribution panel) and therefore the Plessey backplane expects the CPU in Slot 1 and the Multifunction board in Slot 9 and then you start with Slot 2 to fill the system with your cards. I have never heard of such a scheme, but it seems very natural for a small system. So for those that might stumble over a Plessey backplane should first check the BIAKO BIAKI chain.

    It happened to be the case that when I got the system about 30 years ago, all slots were used and hence the CPU was sitting in Slot 1 and the Multifunction board in Slot 9. And when starting with a small system I was thinking that the MF had be next to the last slot used. But this only worked for XXDP but not for RT-11. Also the 50/60Hz input of the connector block was going to the empty slot 9. I thought what a poor design. Then after some testing and also because of my concern regarding the cooling of the CPU I started to fill the system starting with Slot 2, which worked perfectly. But then when I only used the last slots in order to make sure that the MF board was in Slot 9 for the line clock the system again did not boot RT-11, luckily from my PDP-11/Hack and thanks to PDP11-GUI from Jörg Hoppe I had some interrupt test programs. I was suspecting the interrupts because according to the tu58fs output it was loading the full system, but the console did not show any messages. So when I tried the my console interrupt test program it failed. Very frustrated I left my system and went cooking dinner for the family and during that it came to my mind, the backplane must be wired differently and so it was.

    As for the cooling of the CPU, it showed that covering the card-cage with a Acrylglass makes enough air flow from the top of the fan to keep the CPU quite cool (much less than 100°F).

    Now I have a fully working system running RT-11 5.7 with a working LTC.

    P.S. the BDMGO BDMGI chain uses the normal order, i.e. Slot 1->2->3->4..

    Peter

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