"party line" for terminals?

[Richard]

In article <20060317183109.28891.qmail at seefried.com>,
    "Ken Seefried" <ken at seefried.com>  writes:

> That brings back memories.  My first consulting gig almost 20 years ago was 
> with Delta Air Lines working on a system that would tie airline reservation 
> terminals to Unix machines. 
> 
> If those terminals are indeed airline terminals,

They have "Alitalia" stickers on them, so yeah, I think it is most
definately an airline display terminal.  Pictures are here at the
bottom: <http://www.xmission.com/~legalize/vintage/photos.html>; those
are the pictures from the ebay auction, I don't have a photo of the
ports.

> then they likely use ALC 
> (Airline Link Control).  It's a 6-bit, bisync, polled serial protocol 
> derived from some older IBM protocol.  The terminals talked to a 
> concentrator, which then talked to the IBM mainframes running applications 
> on top of TPF.  My project was to replace the concentrators with Unix 
> machines (which could talk to more than just IBM mainframes), with Stallion 
> Technologies providing custom serial cards that could grok ALC. 

OK, so we have a couple possibilities on comm. protocols for this puppy:

    - RS-232 (likely for the DB25 style connectors)
    - RS-422/485 (possibly for the DB9 style connector)
    - ALC (possibly for the DB9 style connector)

When I open up the cabinet housing and look at what kinds of chips are
wired to the connectors, what would be telltale indicators for the
various comm. protocols?  Hrm, thinking about it, maybe it would be
easier if I posted the chip numbers and someone recognized what they
supported?
-- 
"The Direct3D Graphics Pipeline"-- code samples, sample chapter, FAQ:
          <http://www.xmission.com/~legalize/book/>
             Pilgrimage: Utah's annual demoparty
                <http://pilgrimage.scene.org>