[Info-vax] SET TERM /TTSYNC on ancient VMS versions

[Stephen Hoffman]

On 2018-08-15 20:38:55 +0000, hans.huebner at gmail.com said:

> Am Mittwoch, 15. August 2018 20:31:03 UTC+1 schrieb Stephen Hoffman:
>> If you turn off flow control, you'll get communications problems. 
>> Overruns from host to terminal are more common, but there are folks> 
>> that could outrun the receive buffers on some configurations.  And 
>> sometimes the host just isn't ready.  Sooner or later, there'll be 
>> problems with input or output.  Loss, corruptions or whatnot.
> 
> In-band flow control was always a pain in the rear.  Of course, it was 
> also a cheap solution to a problem.  Better async multiplexers and 
> terminal servers, however, had full modem control, and the VMS terminal 
> driver supports out-of-band flow control at least in VMS V5.x.  I would 
> like to know whether hardware flow control was added in V5.x or 
> earlier.  This is out of historic curiosity.

In-band worked pretty well, if the local folks weren't trying to run 
binary data over a serial line.  Or weren't trying to repurpose control 
characters, as was the case with emacs and a few other tools.  Or 
didn't grab specific keys as the device attention request, as a few 
devices still do.  Serial line muxes tended to be... problematic. too.  
Corollaries: don't try to run binary data over a console serial line, 
running asynch DDCMP and SLIP were (still are) messy at best, and make 
sure that terminal or concentrator or mux power-up doesn't generate a 
framing error on the console serial line at power-up; a break signal.  
But i digress.  Support for serial controllers with hardware flow 
control existed in VAX/VMS V3 and V4 and in MicroVMS, and quite 
possibly existed earlier than that.  A serial controller with hardware 
flow control support was required.   Limited modem control and full 
modem control are also supported that far back, though it was generally 
easier to get limited working with a wider variety of gear.  2 to 3 and 
3 to 2 or sometimes 2 to 2 and 3 to 3, 4-5 on each end in the 
connector, 7 to 7, and 6-8-20 wired to 6-8-20 was fairly common wiring 
back then, if the folks soldering were economizing wires.  DECconnect 
massively simplified the wiring mess that existed back then, though 
that lacked support for modem control, which meant that folks were 
still either using their own cabling or with purchased limited or full 
modem control cabling with modems.  But for most serial-connected 
stuff, the DECconnect BC16E cabling and box-specific adapters was 
easier to deal with.  That avoided a whole lot of soldering, 
pin-insertion connectors and related... fun.  We're still occasionally 
dealing with some of the more obscure corners of that era, too: 
https://www.usenix.org/conference/usenixsecurity18/presentation/tian


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