17 Mar
2006
17 Mar
'06
4:16 p.m.
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) From what I've read above (I'd never heard of
it), ALC is a data encoding
protocol. You could send that over an RS232 link, over
an RS422 link,
over a current loop, a TTL-level signal, whatever.
So yes, you might have an RS232 port on this display, but there's no
reason to assume it's going to be a normal 8 bit asynchronous interface
using the ASCII character set (for pedants, I am well aware that ASCII is
a 7 bit code!).
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
If you can identify the drives and receivers connected to the connectors,
you should at least be able to work out the electrical protocol. 1488 (or
75188) is a common RS232 driver, 1489 (or 75189) is an RS232 receiver.
For RS422, look for things like 26LS31, 26LS32
various comm. protocols? Hrm, thinking about it,
maybe it would be
easier if I posted the chip numbers and someone recognized what they
supported?
Go ahead. I've got a number of comms databooks here.
However, this will most likely not tell you the data protocol. There will
probably be a standard serial chip which could be programed by the unit's
microprocessor to do just about any sane format. And the higher-level
stuff -- ALC itself -- is most likely done in firmware. Telling me
there's a particualr seiral chip, microprocessor, ROM, etc will not let
me work out that.
-tony