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

[John E. Malmberg]

On 8/16/2018 4:11 PM, hans.huebner at gmail.com wrote:
> I've read what HELP SET TERM has to say about modem control again:
> VMS V5.5 only implemented hardware flow control on serial lines for
> printers.  It is explicitly stated that /MODEM and /COMMSYNC are
> mutually exclusive and that the latter must not be used for
> interactive terminal lines.
 From my memory:

XON started life as the code to turn on the code to turn on the tape 
reader on a teletype machine and XOFF stopped it.

There is a corresponding set nearby to turn the punch on and off.

The IO abuser's guide has a chart on how the DSR/DTR/RTS/CTS signals are 
used with modem control.  No flow control used there, the RTS/CTS seems 
to shadow the DSR/DTR signals with the exception that the DTR/DSR 
signals are shown to control if the connection is alive.
Could be an implied flow control.

I have seen some third party printers that could be configured to use 
DTR flow control, but that was optional.

I ran into one @&*$@ printer that would drop DTR when it had a minor 
fault.  This printer was on the end of a communications link that used 
DTR as intended.  I ended up doing a special wiring of that port so that 
DTR was on when the printer was powered up.

And I have run into PC terminal programs and third party terminals that 
refused to send characters if the CTS line was not asserted, regardless 
of the flow control selected.

And the MFJ packet modem had the DSR and RTS signals switched on its 
connector, which again required special wiring to connect it to my VAX.

Not to mention what was in one of the DEC System-10 manuals about how 
Control-D was handled by some modems...

Regards,
-John