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Thread: Direct RS-232 Connect
www.piclist.com/techref/io/serials.htm?key=rs%2D232
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face BY : Dana Frank Raymond email (remove spam text)



Tony, it sounds as if you have direct experience with the old model 32 and
33 KSR teletypes. About 20 years ago I attended the CNCP telecommunications
course. CNCP used to service the old electromechanical stuff as well as the
modern transistor based machines as well. The mechanical stuff was
interesting! Pressing a key on the keyboard caused a series of horizontal
sliders with the baudot code to move and a little motorized parallel to
serial converter transmitted the 20ma current loop signal.

In some ways these electromechanical beasts were more of a work of
engineering art then the electronic stuff every was.

BTW the CNCP course was where I first learned the difference between BAUD
and bit rate.

Each technician had to be able to read baudot code right off of the paper
tape, and that was accomplished by about a week of code practice in class -
The instructor would key baudot messages audibly ala ham radio and each
student would hardcopy.

BTW the RS232 BREAK feature was a result of how the electromechanical units
used to work. When a space was detected (start bit) the serial to parallel
motor would advance whether the code was correct or not. Hence, if the
current loop was down it would be interpreted as a repeated sequence of 00H
(NULLs). The print carriage would go up and down but no striker would advance.

To this day most USARTS support BREAK generation.

Anyway, I hope this is not too far off topic fot the list (I guess I'll find
out!).
Regards, Dana Frank Raymond
dfrspam.....icom.ca
<9512081706.AA07525@MIT.EDU>

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