[GreenKeys] Newbie with ASR-35

[Ethan Dicks]

On Sun, Dec 8, 2024 at 5:40 PM Ethan Blanton via GreenKeys
<greenkeys at mailman.qth.net> wrote:
> I think you will find that this is unsatisfactory for computer use;
> the reason is that a Model 35 ASR hooked to a computer will normally
> require three independent loops: two for duplex send/receive
> operation, and a third to activate the paper tape reader for loading
> from paper tape.  (Current loop interfaces for the PDP-11 (at least,
> the DL-11) allow for a primitive form of flow control, where the paper
> tape reader is blocked from reading the next character if there is a
> character already in the serial buffer of the interface.)

For the LT33-version of the ASR-33 for PDP-8 and PDP-11 use, it's two
20mA loops (keyboard and printer) and a not-20mA reader-run-relay pair
for the extra hardware bits in the pedestal.  The LT33 schematics are
in one of the early-70s maintenance printsets (possibly the
PDP-11/20?) but it's just a simple relay in the TTY off of an
additional pair.  No "loop", strictly two-ends-only, from CPU to TTY.
But yes, it fires once per char as a hardware flow control for reading
papertape.

-ethan