XXDP on PDP-11/03
jnc at mercury.lcs.mit.edu
Wed Aug 14 09:17:24 CDT 2019
> 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 BPOK)
has to be hit.
The KDF11-B and all KDJ11 machines do have the LTC register, which operates
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