Terminals...

[Johnny Billquist]

Dave McGuire <mcguire at neurotica.com> wrote:
> On 8/13/10 4:27 AM, Johnny Billquist wrote:
>>> >>   Not at all, I just wanted to know what he didn't like about them.  The
>>> >> only thing I dislike about VT420s is the non-removable power cables.
>> > 
>> > Huh? My VT420s have removable power cords...
> 
>   Mine do not.  This is interesting.  I know there was a variation of
> the VT320 (yes 320) that had a removable power cord, but they're not
> terribly common.  Apparently there's a removable-cord version of the
> VT420 as well.  Interesting!

Hmm. Unfortunately I don't have any VT320 around anymore, since all of 
them have broken down (flybacks mostly). But I've had atleast five of 
them over time, and all have had removable cords.

I wonder if this might be more of a european thing. Since different 
countries in Europe use different power plugs, it makes sense to have 
the power cord detachable. There is more or less a standard format plug 
that goes into any kind of computer equipment, but the wall plug differs 
between countries. So you usually don't use a fixed power cord, but 
instead the standard equipment power connector on your equipment, and 
then ship whatever power cord is used in that country.

>> > The VT420 have both DB25 and MMJ, so I can't see how that could annoy
>> > anyone. (As do all DEC terminals from the VT220 onwards.)
> 
>   Now waitaminute.  I am staring at the back of both a VT420 and VT320
> right now, on the table opposite my desk.  Neither of them have DB25s,
> only MMJs.  The VT420 has what looks like a knock-out that's about the
> right size for a DB25.
> 
>   Apparently versions with and without DB25s exist as well!

Apparently so. :-)

>   That same (rare-to-me) VT320 I mentioned above that has a removable
> power cord also has a DB25.  Out of a few hundred VT320s that have gone
> through my hands, it's the only one I've ever seen that has either a
> removable power cord or a DB25.  I've never seen a VT420 with either of
> those, and until now, I haven't even heard of their existence.

Well, I have four VT420 at home right now, and they all have both a DB25 
and detachable power cord. Since I was feeling creative tonight, I even 
took pictures of the back side of all terminals I have at home.
So here is a link to where you can see the backside of:
VT-330, VT-420, VT-510, VT-520 and VT-525. All of them have DB25 and all 
of them have detachable power cords.

http://www.update.uu.se/~bqt/vt

(Argh, I just realized I missed the VT-240 I have, but oh well...)

William Donzelli <wdonzelli at gmail.com> wrote:

>> > Huh? My VT420s have removable power cords...
> 
> Some do, some do not.

Yup. I just learned. All I've ever seen have been with detachable cords. 
But as I wrote above, I bet this is a european thing.

>> > The VT420 have both DB25 and MMJ,
> 
> Some do, some do not. Of the fifty or so I had recently, I think only
> one had the DB25 in addition to MMJ.

All mine do, and I have four right here.

>> > However, MMJ is actually very nice. Too bad it didn't catch on outside of
>> > DEC. But I try to use it for everything I can at home.
> 
> MMJ "fixed" a problem that really was no big deal - people confusing
> RJ45 serial with ethernet. I think the real reason was to lock people
> into MMJ by doing the old lets-violate-the-standard trick. In my book,
> DEC is guilty as anyone else here.

Huh? That is totally backwards in more than one way.
Yes, MMJ "fixed" one thing. It has nothing to do with ethernet, but all 
to do with people (and companies) who couldn't figure out how to wire a 
DB25. Almost all companies got the gender wrong on their equipment. In 
addition to that, many couldn't figure out what a DTE and DCE was.
Now, that is called standard violation. Causing people to have cables 
they think they can connect, but which don't work. DEC is one of the two 
companies that did get it right (the other one being HP). To this day, 
it totally amaze me how so many companies couldn't get this right. And 
from that perspective it don't surprise me when people around here don't 
get it either (there was a long thread not long ago, which I declined to 
even participate in). RS-232 is so simple that it's hard to get wrong. 
There is only two things you can mess up with. Connector gender, and DTE 
vs DCE. How can people find that so difficult???
And if people and companies had actually stayed with the standard, you 
wouldn't even had been able to mix those to parameters up.

A DTE *should* have a *male* DB25. A DCE *should* have a female DB25. A 
male-male cable should be crossed, a female-female cable should be 
crossed, a male-female cable should be straight. There is nothing more 
to it.

All terminals and computers are DTEs. Modems are DCEs. But it you 
absolutely wanted to, feel free to wire a modem up as a DTE. It will 
work just fine, just as long as you fit the right DB25 to it, and wire 
it up accordingly.

But no. Companies just loved putting female DB25 on their terminals, and 
wire them up as DTEs. Or put male DB25 on their computers, and wire them 
up as DCEs. *Idiots*

That is called violating the standards.

And to make matters ridiculously worse, we have IBM. Who simply put just 
raped the RS-232 standard by using a DE9, moving one or two pins in a 
totally non-logical way, changing the gender, *and* sortof wiring it as 
a DCE.
They should be taken out to the back and shot. IBM have caused more 
damage to the computer world than all other companies put together.

Here is a simple tip for the next time you wire a RS-232 up. Measure pin 
2 and 3 on the equipment. One should at around -12V, while the other is 
around 0. Do this on both sides. Then wire the -12V from one side to the 
0V on the other for both 2 and 3. And run pin 7 straight through.
And that's it. You now have a correct RS-232 cable, albeit just the data 
leads. You can wire the rest up if it amuse you. The most important ones 
are DCD, DTR, DSR, RTS, CTS. For a DTE-DTE, you should wire CTS to RTS 
and DCD+DSR to DTR. Very simple. And if I remember right, we're talking 
about pines 4,5,6,8 and 20. But I'd usually check the RS-232 DB25 
connector layout before I try to wire a full cable up. Most of the time 
I'm happy with just 2,3 and 7 anyway, since I don't do hardware flow 
control (another RS-232 standards violation, by the way, and which DEC 
did not do). But having the DSR signal is useful to detect if someone 
gets disconnected.

What DEC did with MMJ was in no way violating any standard. Noone in his 
right mind would think that an MMJ was an RS-232. So what standard did 
they violate (if I may ask?). Hmm, I seem to remember that the 
signalling in the MMJ is even called DEC-423, but I might be remembering 
wrong. It is pretty much compatible with RS-423 anyway (might be 
equivalent), and you can usually get away with connecting that directly 
with RS-232, but they are not really the same thing. (Hmm, looking at 
RS-423, it would appear that DEC-423 is a superset, since DEC-423 don't 
actually use a common ground for everything, but use one ground for all 
transmitted signals, and one ground for all received signals).

So, the signalling in the MMJ connector is only claimed to be 
communicating using DEC-423. How would that violate any standard? If DEC 
had said that it was an RS-232 port, then they would have violated the 
RS-232 standard. (I guess I'm confused at your definition of violating a 
standard.)

What MMJ solved was that they removed the gender issues, and they 
simplified the DTE/DCE issues. Your cable is either straight or crossed 
(either flat or turned 180° looking from one end to the other). They 
also simplified the assembly of the cables compared to RS-232. The fact 
that MMJ

Ethernet vs. RS-232 on a RJ45? Give me a break. None of that even 
existed when the MMJ came about. And the idea of putting RS-252 on an 
RJ45 is something I'd call violating a standard, if anything. But it 
comes with the one-connector-for-everything that some people are so fond 
of. So you also have telephony on RJ45, to make life really 
interesting... And all running through one patch panel.

>> > The reliability of the VT420 seems to be pretty decent. I've had many more
>> > VT320 fail on me. But we have to remember that we're talking about 20+ year
>> > old equipment now...
> 
> Yes, but these were built well towards the end of the monochrome CRT era.

I don't know. When was the end of the monochrome CRT era? Has it ended yet?

Dave McGuire <mcguire at neurotica.com> wrote:
> On 8/13/10 5:51 PM, Johnny Billquist wrote:
>>> >>   AFAIK the VT420 supports Sixel, but not ReGIS.
>> > 
>> > No. The last graphic terminal was the VT340.
>> > The VT420 don't support any graphics, unless you count the user defined
>> > font as graphics.
>> > 
>> > Graphics implies either SIXEL, ReGIS or both. Actually, I've never seen
>> > any terminal that supports sixel but not ReGIS, however, several
>> > printers is of that inclination.
>> > 
>> > (Although I'm sure someone will now recall some terminal that do sixel
>> > but not ReGIS just because I wrote the above...  :-)  ).
> 
>   I've never *used* Sixel graphics on a VT420, but the manual clearly
> states that it supports the Sixel format.
> 
>   (flip flip)
> 
>   Ok, I just went back and re-read it.  It "supports Sixel format" as a
> way to encode user-definable character sets.  So you're right I suppose,
> it ALMOST supports Sixel graphics!  ;) 

I said "unless you count the used defined font". :-)

All that said, I know some crazy person wrote a GIF viewer for the 
VT320, using the user defined font to pull it off.

Dave McGuire <mcguire at neurotica.com> wrote:

On 8/13/10 8:49 PM, William Donzelli wrote:
>>> >> However, MMJ is actually very nice. Too bad it didn't catch on outside of
>>> >> DEC. But I try to use it for everything I can at home.
>> > 
>> > MMJ "fixed" a problem that really was no big deal - people confusing
>> > RJ45 serial with ethernet.
> 
>   Huh?  I don't see how that can be.  The 802.3i standard which defined
> 10baseT Ethernet on RJ45 connectors came out in 1990, while the first
> terminal to implement MMJ was the VT320, which predates that by three years.

Ouch. You're right. For some reason I was thinking that the VT220 also 
had MMJ, but it didn't. That only came with the VT320...

But I can't see the relevance of MMJ vs. RJ45 either, for various 
reasons mentioned above.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol