
Transmission Methods
NOTE: Keep in mind that the
Contact (Point) I.D.
formats and
the
Superfast
formats (e.g.,
ADEMCO, FBI,
and
Acron
)
have unique ways of reporting data, which are not
shared by the generic formats listed on page B-2.
As implied by the table on page B-2, the data used in
subscriber messages is encoded and carried over the
telephone network through the use of several methods, each
of which has its own advantages and disadvantages. These
methods are briefly discussed below.
"Pulsed" Communications
Many formats use common "rotary pulses" to convey the data
that comprise the message. Were you to listen (over a
telephone line) to a typical
3x1
report (using "rotary pulses"),
you would hear groups of "clicks" much like those produced
by a rotary dial. When processing such a format, the receiver
counts the clicks in each group, assembles the data, and
(depending on the format) decodes it, displays it (if the CP-
220A is in the MANUAL Mode), and forwards it to the
printer and the Automation System, if available. Pulsed
formats were among the first used in digital communications,
and they are still in common use today. As the receiving
equipment became more sophisticated, a greater number of
pulses could be accurately processed, permitting a greater
"throughput" of data into the Central Station. Today,
40
pulses per second
(pps) is not uncommon, and is used by
several "pulsed" reporting formats.
DTMF
(Dual Tone Multi-Frequency)
DTMF
is also in common use today, and is incorporated into
the formats developed by several manufacturers. These
formats use the
TouchTone
® system to represent data in
much the same way that the individual digits in a phone
number are represented by mixing pairs of frequencies;
hence, the term
Dual Tone Multi-Frequency
. Unlike the
TouchTone
® system employed in our telephones, the use of
DTMF
must be extended to include the equivalents of the
hexadecimal characters from "A" through "F."
NOTE: An understanding of the hexadecimal numbering
system would be helpful. If you are unfamiliar with
"hex,"
Appendix A
will provide the basics.
CP-220A Central Station Receiver Appendix B:
Page B-5
Hook-Up and Installation Manual
Communication Formats