ISO: PDP-11/40 LTC and Stack Limit options

Noel Chiappa jnc at
Mon Nov 21 18:04:42 CST 2016

    > From: Josh Dersch

    > I'm finally turning my attention back to my 11/40 (which I started
    > working on 7 years ago and never quite got around to finishing -- I've
    > learned a lot since then and I'm hoping to be able to debug it properly
    > now).

A KM11 might help, if you have one: there are a couple of sources for new ones
(I got mine from Guy), it will allow you to single-step the microcode, etc,
    > My ultimate goal is to run V6 or V7 UNIX on it -- I have the MMU but
    > I'm looking for an M787 (line-time clock) and M7237 (stack limit
    > register) to complete the set. 

You don't need the SLR to run Unix V6 (in fact, IIRC, it doesn't use it). For
the clock, you don't absolutely have to have a KW11-L, you can substitute a
KW11-P - but V6 _has_ to have one or the other, or it panic()'s - some things
in the kernel have to have a working clock.

You will also need the KE11-E (M7238), as the Unix C compiler emits MUL, DIV
etc, and even the bootstrap uses them. The KE11-F (M7239) is useless; the V6
Unix C compiler doesn't generate that type of PDP-11 floating point.


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