XXDP on PDP-11/03

systems_glitch systems.glitch at gmail.com
Wed Aug 14 09:24:29 CDT 2019

Yep, fun times on LSI-11/2! Some configurations also won't boot unless it's
on, if I remember correctly. I suppose this is part of the reason that
LSI-11/2 CPU boards are so cheap!


On Wed, Aug 14, 2019 at 10:17 AM Noel Chiappa via cctalk <
cctalk at classiccmp.org> wrote:

>     > From: Paul Koning
>     > Isn't the interrupt disabled by RESET?
> Nope. On the -11/03 and KDF11-A, BEVNT is wired straight into the CPU, and
> there's no internal register to control it.
> The BDV11 does have a register which can enable/disable the LTC (it
> connects
> BEVNT to ground via a transistor when the appropriate register bit is
> cleared); but, ironically (given your question), BINIT/RESET does _not_
> clear
> that register! Only BPOK does. (My theory is they were short of a bus
> receiver
> for BINIT, and rather than put a whole extra chip on the card...) So, once
> on,
> it has to be explicitly turned off, or the 'boot' switch (which toggles
> has to be hit.
> The KDF11-B and all KDJ11 machines do have the LTC register, which operates
> 'correctly'.
>         Noel

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