🚀 go-pugleaf

In article <1991May17.222410.26944@MDI.COM>, mitchell@MDI.COM (Bill Mitchell) writes:
>>[...]
> 
> Be fair now.
> 
> The +++ mechanism allowed users and application writers to manipulate
> the modem without having to worry about how to twiddle hardware control
> lines.  If you could talk _thru_ the modem, you could talk _to_ the
> modem.
> 
> That's a _big_ advantage over not being able to control the modem unless
> you could find a way to twiddle the control lines in some strange way.
> I remember a modem (I've forgotten who perpetrated it upon me) which
> expected to be talked _thru_ with RTS asserted and talked _to_ with
> RTS released.  Drop RTS, give it commands to dial the phone, raise RTS
> to talk to the other end of the link, drop RTS to give it more commands,
> etc.; and I remember the hassle these things caused.  Hayes "+++" was
> like a breath of fresh air.

I've come in late on this discussion (I'm going to hear RMS on his UK 
tour tomorrow).  However, if the existence of +++ is the substance of 
the Hayes patent, then anyone with enough money and the will can 
certainly sue on the grounds that the patent is invalid on account of 
prior art.  The operating system of the Titan computer here, completed 
in the mid 1960s, implemented just such a mechanism for switching the 
interpretation of Paper Tape Reader data from data back to control.

The feature was widely copied, and certainly published over and over 
again in manuals by the University Mathematical Laboratory (as it then 
was).  Unless the Hayes claim is minuscule in
its extent (i.e., says nothing more expansive than `we claim the
following thing for switching _modem_ data stream interpretation'), it's
almost certainly invalid. 
-- 
Robin Fairbairns, Senior Consultant, postmaster and general dogsbody
Laser-Scan Ltd., Science Park, Milton Rd., Cambridge CB4 4FY, UK
Email: robin@lsl.co.uk  --or--  rf@cl.cam.ac.uk