PDP-11/70 Boards

[Ed C.]

Very helpful! Thank you

On Tue, Nov 30, 2021, 19:06 Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:

>     > From: Ed Cross
>
>     > I'm currently restoring a PDP-11/70 system and need the following
>     > boards to complete the CPU: FP11-C
>
> From your mention of the FP11-C, I gather your -11/70 has a KB11-C (later)
> CPU, not the KB11-B CPU of the earlier PDP-11/70's (prior to 1976 - the
> difference between the two was whether they took the optional FP11-B or
> FP11-C
> FPP).
>
> Not that it makes a big difference in your case; the 4 cache cards are the
> same in both.
>
> There used to be a seller on eBait (on the mid-East Coast - Baltimore,
> IIRC)
> who was selling -11/70 CPU cards (I bought a whole spare set from him) but
> alas he seems to have gone away (or sold them all; a quick search, both on
> eBait, and in my email, didn't turm him up; I can institute a deeper search
> if need be).
>
> From the blog of someone who got a KB11-A working, you'll really need KM11
> cards; dunno if Guy Steele still has those clones he was selling.
>
>
> There are definitely some versions of Unix which will run fine on -11/70's
> without the FP11 (e.g. V6). The system binary is different for the
> with/without versions, though: in the assembler code which saves the state
> of
> one process before switching to another, there is code like:
>
>         stfps   (r1)+
>
> which will probably get an illegal instruction trap in kernel mode on a
> machine with no FP11, and is therefore conditionally assembled (depending
> on
> if the particular machine the system is being built for has an FP11).
> Perhaps
> the later BSD versions look for the FP11 on startup, and adjust their
> behaviour appropriately, but I'm not familiar with them.
>
> V6 as distributed contains system binary for an -11/40, which will run on
> _any_ -11 UNIX will run on, and can be used to build appropriate system
> binary.
>
>
> (Diversion: I've never found out whether the KB11-B and KB11-C of the
> -11/70
> used/could use the same backplane or not. By examining the prints for the
> boards of the FP11-B and FP11-C, and seeing on which pins they exchanged
> signals, and what signals they exchanged with the rest of the CPU, and on
> which pins, it should be possible to work it out. Ditto for the M8133 ROM
> and
> ROM Control of the KB11-B, replaced with the M8123 in the KB11-C.)
>
> (Interesting factoid: the M8123 is the only card shared between any variant
> of the -11/45 and -11/70: both the KB11-C and KB11-D use it. Of course, I
> think we're still missing a wirelist for the -11/70 backplane, of any
> variant; and the ECO history. There appears to have been at least one
> poorly
> documented upgrade; see here:
>
>   http://gunkies.org/wiki/MK11_memory_system#CSR_Access
>
> for more.)
>
>         Noel
>