[Info-vax] Terminal emulators, was: Re: Monitor for Alphastation 500

[Michael Moroney]

Simon Clubley <clubley at remove_me.eisner.decus.org-Earth.UFP> writes:

>On 2019-09-12, Jan-Erik Söderholm <jan-erik.soderholm at telia.com> wrote:
>> Den 2019-09-12 kl. 20:21, skrev Arne Vajhøj:
>>> On 9/12/2019 1:48 PM, Simon Clubley wrote:
>>>> On 2019-09-12, Arne Vajhøj <arne at vajhoej.dk> wrote:
>>>>> On 9/11/2019 6:23 PM, Jan-Erik Söderholm wrote:
>>>>>>
>>>>>> Agree, Putty works fine enough. Have used it for all my VMS work,
>>>>>> both hobbysit and professional, since 10+ years back. No issues.
>>>>>> Before that I used WRQ Reflection for 20 years. The best of the
>>>>>> commercial alternatives....
>>>>>
>>>>> I think all emulators today works OK for standard stuff.
>>>>
>>>> Provided "standard stuff" doesn't mean trying to use EVE/TPU or EDT. :-)
>>>>
>>
>> Why would not EDT work using something like Putty?

>If you carry on reading :-), you will see that I was talking about
>terminal emulators running on Linux, not Windows, and that I stated
>pterm, which is a xterm style packaging of PuTTY, was one of the
>two emulators I had tried on Linux which were usable with VMS systems.

The escape sequences used by VMS editors, SMG and others have ANSI definitions
but there are also many parts of the ANSI spec not well implemented.

For example, for cursor positioning, there is an escape sequence which sends
the vertical and horizontal screen positions separated by the ";" character,
which is defined as a parameter separator in the ANSI definition.

The problem is, the ANSI definition states that if a parameter is not provided,
it defaults to 0. The cursor positioning command takes two parameters, line and
column, and the ANSI definition also specifies that for it, 0 is the same as 1.

However, EDT and other programs use a shortcut. They transmit fewer characters
when they can (important when dialed in at 300 baud!) So if either the row or
column is 1, EDT skips the parameter (and the ";" if the second parameter) and
the missing parameters are supposed to be interpreted as row/column 1. But some
emulators don't parse that correctly.

In addition the terminal emulators usually only have an option "VT100" or "VT220"
or something like that.  When this is done the programs may assume the DEC 
extensions work, but most emulators don't have them... 

Add similar problems elsewhere...

(I am very familiar with that because ages ago I had a Heathkit H-19 terminal that
would work with EDT except for this specific bug, not parsing a cursor position
command without both parameters specified)