5 Oct
2026
5 Oct
'26
6:14 p.m.
Hi Chris:
Don't see why it wouldn't work on a 2020, but someone with a 36-bit machine
will need to test it.
I think your expectations of the possible drive shrinkage factor are a bit
off... :-)
While a solution that fits inside a terminator would be convenient, it just
is not possible. You could, however, run ribbon cables directly from the
Massbus transceivers (usually M5904s) to the emulator and hide the emulator
inside the rack somewhere.
My eventual goal is to reduce the emulator to a three-board "sandwich" that
takes the place of the M5904 trio on systems that use it. That eliminates
the differential drivers and receivers and simplifies the electronics quite
a bit. Also solves the problem of "where do I put the emulator at?" :-)
Something like this:
https://www.dmv.net/mbe/RS06_Setasi.pdf
Jim
On 10/5/26 19:57, Chris Zach via cctalk wrote:
Jim:
Nicely done. If it runs on a 2020 this will finally be a game-changer. :-)
Can it be built into a Massbus terminator plug? That would be a proper
mounting....
Chris
On 10/5/26 18:00, Jim Bender via cctalk wrote:
>
>
> It's been a while since my initial posting about this project but it is time
> for an update.
>
> This has been mostly a spare time project, and you know how life tends gets in
> the way sometimes...
>
> The work itself has been a bit of a "maze of twisty little passages, all
> alike" with many potholes and obstacles, but progress has been made.
>
> The video below tells the tale:
>
> https://youtu.be/KwaNschJg6w
>
>
> Synopsis:
>
> A real PDP-11/70 boots RSTS/E V10.1 through it's unmodified RH70 controller
> with the data coming from the Massbus emulator.
>
> Operation is rock solid and so far have not been able to break it. It also
> passes the ERHAE1 XXDP diagnostic without errors.
>
> We now have a viable option for modern storage for Massbus systems.
>
> Still to do is performance optimizations, hardening against some edge cases,
> and a large amount of code cleanup.
>
> I only have a PDP-11/70 to test with, but it *should* work with any Massbus
> system. Adherence to the DEC Massbus Specification was strict and every
> attempt made to make it behave as a proper Massbus device rather than just
> coding things to make the RH70 happy.
>
> I am kicking around the idea of putting together a blog chronicling the
> various trials, tribulations and milestones encountered along the way if
> anyone is interested in reading the gory details....
>
>
> Cheers!
> Jim