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Microcomputers As A Space Spinoff 3846


Microcomputers As A Space Spinoff 3847
The obvious thing was as a "solid state drive". I certainly saw at least two of...

alt.folklore.computers

The downside was that they shut down on PF more often than a machine not equipped with PF interrupt.

I used PDP-8s as embedded controllers for power station stuff. The original intent was that a process control machine would run on inverter power with human intervention to restart after PF. A data logging machine would run on the mains with PF interrupt and restart where it left off. Fortunately, on the -8, the PF circuits are on a separate card. No card, no PF functionality.

Without the PF stuff, the machine shuts down when the DC rails are too low. It just needs sufficient stored energy to ensure that the last instruction completes its memory cycle. With PF, AC input is monitored, such that on failure a shutdown is irrevocably initiated but with a guaranteed N millisec of normal operation before DC low for the PF interrupt service routine. It's a clever guy that can design the AC low detection to ignore transient voltage depressions, but catch real power fail. I'll admit to being a bit paranoid on this, but it's difficult to find electrical environments noisier than in a power station. On test, we averaged two PF trips a day on a logger, none on the controllers on inverters. Bypbutt the inverters to mains, still no failures. Put a PF card in a different machine and the problem followed the card. Back to the drawing board for a re-think on logger power.

The sad thing is that later when minis had DRAM memory, the PF interrupt had become standard. All PDP11s shut down on AC low, and can trap to 24 on PF (presumably for those with battery backup enabled on the memory cards). Not the way to go for process control kit, all of my Qbus stuff ran direct from 24VDC.

Regards,

David P.


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