PDP-12 at the RICM (Michael Thompson)

Michael Thompson michael.99.thompson at gmail.com
Sun Aug 2 09:19:52 CDT 2015

With a lot of help from Dave Gesswein and Warren Stearns we were able to
get the MARK12 PDP-12 tape formatting program off a LINCtape and int paper
tape format. Running it showed that a diode on the field-0 core stack had
failed during the week making memory in the range of 4000-5000 unusable.
Fortunately we had a spare core memory stack so we were running again in a
few minutes. We have traced and replaced diodes on core stacks before, so
we will fix the broken core stack.

We were able to format a LINCtape, but running it without a video display
was a little challenging. The tape diags work better with the reformatted
LINCtapes, but still not perfectly. It looks like there is an issue in the
selection logic in the TU56. That should not be difficult to debug and fix.

We booted LAPS6-DIAL from LINCtape. The VT14 display is not working yet, so
we were driving blind. We could see some fuzzy characters displayed on an
oscilloscope so we could see that our typing was actually getting handled
by the editor. We tried three different oscilloscopes, but none have an
intensity or blanking input so the display was not readable.

We couldn't find any documentation for booting OS/12 from LINCtape, so
Warren looked through an octal dump and found that block zero is the boot
block, just like OS/8. The OS/12 boot block starts at 0020 like many LINC
programs. Since this uses the serial console we were able to interact with
the OS normally.

This is the first time in 24 years that an OS has been run on this system.

Michael Thompson

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