[GreenKeys] Newbie with ASR-35

[Ethan Blanton]

David S wrote:
> There are a few interfaces out there that you could use, but I ended up with
> the deramp model.  I am waiting on a DB9 to RJ11 to complete that setup, but
> it looks like deramp makes a Model 33 interface - Teletype RS-232 Adapter
> <https://deramp.com/tty_adapter.html> that may work on yours.

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.)

That said, Alan's serial interface _probably_ has native current loop
support with a power supply and all three signals, and only requires
the wiring to the Teletype to make it go.  I understand that using the
power supply on the adapter board is a little tough on the board, so
disabling current generation in the PDP-11 and using an external loop
supply (with three outputs!) may be indicated.  12 V at 20 mA each
should be plenty.

Ethan