Strange Terminal Emulation Problem

I had a strange one the other day. Using Alphacom over a serial line to a SCO machine and the only way it would work was if the emulation was VT100.

Details: I could attach an old Wyse60 terminal to the same line and it worked fine no matter what emulation was chosen. With the PC, however, even changing emulation after logging in, with or without a tset, would send the screen insane - looked to me like the baud rate had suddenly changed. I found that I could still type commands, and doing an stty -a redirected to some file showed that nothing had changed on the Unix side (as expected). I was blaming a bad download of Alphacom, but then I tried regular old Windows Hyperterminal; this looked like it was having communication trouble: dropping characters, some characters set to high bit, etc. I cut the wiring to its basics (2,3,7) but no change.

So my assumption was and is a bad serial card - but why would vt100 work? I could even do long ls -lR's without a glitch.. this has me puzzled.

Click here to add your comments




Sat Feb 19 18:09:11 2005: Subject:   TonyLawrence


Fortunately, vt100 was sufficient for the app that needed to be run here.





Mon Feb 21 16:03:35 2005: Subject:   BigDumbDinosaur


Maybe the serial card drivers are somehow mangling the non-VT100 escape sequences. Since every VT100 escape sequence begins with a CSI ($1B $5B or <ESC> [), it's possible the card drivers expect to see the left bracket as the next char after <ESC> and consider anything else to be bogus.



Mon Feb 21 16:28:04 2005: Subject:   TonyLawrence


OK, but what business does a serial card driver have looking at escape sequences?





Mon Feb 21 18:27:41 2005: Subject:   anonymous


I'd suspect the *unnamed* serial card driver also. You could prove this by connecting to the standard COM1 or COM2 ports and seeing if you can replicate the problem. Perhaps the flow control is set to something non-standard like PC-TERM or hardware (DTR) flow control, and is being mangled by the driver.

I don't understand your remark that you could plug in a Wyse 60 terminal and have it work no matter what the emulation was set to. Are you referring to the emulation the terminal itself is setup to, along with a corresponding change to the TERM in the shell session? Or are you saying that if the terminal is using native wyse60 emulation, you could set the TERM environment variable to anything you'd like and it would still work?

It's also possible you've stumbed upon a minor Alphacom bug. Make sure you're using the latest build of version 5 or version 6.

--Bob



Mon Feb 21 19:24:48 2005: Subject:   TonyLawrence


I meant, of course, that I could set the dumb terminal to any of its possibilities, and make the corresponding TERM change at the host, and all worked as expected - in other words, its not the wire or the digi or the host.

My suspecion is that the machine itself is whacked. I did try com1 also, with the noted result - partially garbled characters. Not as bad as on the PCI serial card, but bad stuff. I also used Hyperterm with the same problems, so it's not Alphacom either. Very, very puzzling..



Don't miss responses! Subscribe to Comments by RSS or by Email

Click here to add your comments

If you want a picture to show with your comment, go get a Gravatar

Buy Take Control of the Mac Command Line with Terminal

Buy Take Control: The Mac OS X Lexicon

Buy Take Control of Screen Sharing in Leopard

Buy Take Control of Permissions in Leopard

Jump to Comments

Many of the products and books I review are things I purchased for my own use. Some were given to me specifically for the purpose of reviewing them. I resell or can earn commissions from the sale of some of these items. Links within these pages may be affiliate links that pay me for referring you to them. That's mostly insignificant amounts of money; whenever it is not I have made my relationship plain. I also may own stock in companies mentioned here. If you have any question, please do feel free to contact me.

Specific links that take you to pages that allow you to purchase the item I reviewed are very likely to pay me a commission. Many of the books I review were given to me by the publishers specifically for the purpose of writing a review. These gifts and referral fees do not affect my opinions; I often give bad reviews anyway.

We use Google third-party advertising companies to serve ads when you visit our website. These companies may use information (not including your name, address, email address, or telephone number) about your visits to this and other websites in order to provide advertisements about goods and services of interest to you. If you would like more information about this practice and to know your choices about not having this information used by these companies, click here.