[GreenKeys] Special sequences

[cswiger]

Aha - I've wondered about some character sequences we
sometimes see here. Now I found a book at the last
hamfest which reveals all:

The use of Sequences of Telegraph Characters for Special Purposes

Start of message        ZCZC

End of telegram         ZZZZ  or
                        ++++        Used in retransmission systems
                                    and store and forward devices.
End of message          NNNN



Suppression of delay
signals                 HHHH        Used to prevent the retrans-
                                    mission of delay signals used
                                    for error-corrected radio-
                                    telegraph channels


Connection of re-
perforator or
equivalent device      CCCC         Switching into the circuit by
                                    remote control a reperforator
                                    or equivalent device


Disconnection of
reperforator or
equivalent device      FFFF


Connection of
data equipment         SSSS



Source: "Telecommunication and the computer", James Martin, 1969