RF08/RS08 emulation

Ethan Dicks ethan.dicks at usap.gov
Thu Aug 7 16:51:42 CDT 2008

On Thu, Aug 07, 2008 at 02:27:19PM -0700, Vincent Slyngstad wrote:
> From: "Ethan Dicks" 
> >Ever since I got that first PDP-8/L when I was in high-school, I've
> >been trying to get a OS/8-capable configuration.  I've gotten as
> >far as an -8/L w/12kW (via a BM08) and PC8L high-speed papertape,
> >but no posibus mass storage.  My negibus -8/i has 64kW of DF32,
> >but only 4kW of core (another long-term project is to get that up
> >to 8kW internally). 
> There are some bus converter projects there too, if those would be 
> of any help.

Sure, if it comes to that.  The -8/i is out of the picture until I
get enough memory on it anyway.  I have enough M-series logic to
stuff the backplane with the memory extension logic (somewhere, I
even have an M720), and I think I have enough spare G-series
logic from an -8/L that came to me as a crate of parts (broken
chassis, no front-panel, a few broken backplane pins, no core...),
or nearly enough to implement 8kW, but 32kW sure would be nice for
doing any "real" work (like playing Adventure ;-)

My main -8/L is in closer shape than anything, though if I fix
whatever is wrong with my -8/e, I do have a posibus adapter for
that, and it might be a more reliable testbed for new devices,
especially since I can easily throw an RX8E in there (borrowed
from a PDP-8/a-based WPS box in the same room).  I suppose I
could just use the -8/a and the posibus adapter, but that, too,
has some odd problem (with the KM8A, IIRC).

Sigh... all of this stuff worked once, but it's been three
moves and a lot of years, and I haven't been able to spend
enough time in front of the machines to give them the attention
they deserve.

> No particular reason, but the board's pretty crowded trying to get 
> it all to fit in 8"x11".  I'd probably use SIL resistor packs and 
> shift down the six DIPs below the switches.  (I'm not sure there'd 
> be enough void left to route the thing with 10mil design rules.)

Sounds crowded.
> There's some other "fast and loose" stuff in there too -- S240 as 
> bus drivers, multiple LS loads on the bus (still should be less 
> than a 74xx load), and (importantly) no provision to continue the 
> bus, so that it must be placed last.  There's also no equivalent 
> for the G717 terminator card, so it may need to be a fairly short 
> bus!

Well... while that's not optimal, it's workable.  Given the dearth
of OEM posibus equipment these days (I have none and have never
seen any except on the web), it's not like many people are going to
be sticking this on a heavily loaded bus.  The RF08 is large enough
to do interesting things with, leaving only removable media to get
things on and off the system - paper tape is certainly one way,
but floppies are more convenient... in my particular case, I suppose
the largest configuration I'd attempt would be a modern solid-state
RF08 and that RX8 you/we started and haven't gotten back to.  It's
been so long that I can't remember if the RX8 can be in the middle
of the posibus or not.


Ethan Dicks, A-333-S     Current South Pole Weather at  7-Aug-2008 at 21:30 Z
South Pole Station
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Ethan.Dicks at usap.gov            http://penguincentral.com/penguincentral.html

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