On Sat, 9 Sep 2017, Steve Johnson wrote:

> Part of that problem was probably electronic, not software.   Many of 
> the early terminals were half-duplex.  The normal mode was that the 
> terminal typed what came over the line, and the keyboard was locked.  If 
> you wanted to let the terminal send data, you needed to send a control 
> character to unlock the keyboard, and then another one to lock it when 
> you wanted to send data again.

Aah, well I remember the times that I felt like leaning over to hit
the Big Switch on our 360/50, when the console jammed...

That was the Blue Button, of course, not the Red Switch (we weren't 
allowed to pull that).

-- 
Dave Horsfall DTM (VK2KFU)  "Those who don't understand security will suffer."