Andy's mention of the 'old pacing characters on XTs' reminds me
of where I first saw stop bits.

Back in the mid '60s through about 1982, the old Teletype KSR-33
was in widespread use. The advent of PCs pretty much wiped them out
within a few years. These were electromechanical keyboard/printer
terminals, As Seen On TV In Old Movies. They ran 110 baud (11cps)
and as I recall used two stop bits.

My recollection was that if you tried to use them with one stop bit,
there wasn't enough time between successive characters for the cam
assembly to get all the way stopped after each printing stroke, and
it would cause the output to get all messed up. These things ran on
a solenoid selector and cam arrangement that rotated and lifted a
cylindrical printhead. At the end of the character, a 'club' whacked
the printhead into the ribbon and made the impression on the paper.

The other thing I recall was the end-of-line handling, which as I
recall needed a 'null' character appended for my particular TTY. That
gave the printhead carriage enough time to return to the left hand
side of the platen before the next character arrived. That's why CR
and LF are separate characters; CR moved the carriage back, and LF
caused the platen advance solenoid to kick the paper up one line. If
you didn't add the null, the next character would print while the
carriage was still moving to the beginning of the line.

When I worked in the radio business, we had an even older teleprinter,
used for UPI wire copy. This one ran at 50 baud. Caps only, of course,
as were the KSR-33s. We also didn't have a lot of the nifty characters
in use today, (like backslash, tilde, etc.) but on the Unix systems of
the time, we made do with funny looking escape sequences. Alas, I don't
remember what they were, but you could go take a look at the source
for a TTY device under Unix, and you'd find it. Ah, the good old days....

NOT!

Mark G. Forbes, R & D Engineer  |  Acres Gaming, Inc.    (541) 766-2515
KC7LZD                          |  815 NW 9th Street     (541) 753-7524 fax
forbesm@peak.org                |  Corvallis, OR 97330
http://www.peak.org/~forbesm
mforbes@hq.acresgaming.com

"There has been an alarming increase in the number of things I know nothing
about."
---Anomalous