Telesto Private Wire, Manual

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levels, voltages, bit duration, etc. In order to efficiently couple the RS-232 data to the telephone
network a device known as a modem (MOdulator/DEModulator) is used to transform the RS-232
digital data into an analog signal which can be efficiently carried on the telephony channel. By
varying the properties of the analog signal such as signal amplitude, phase and duration, one can
efficiently pack the RS-232 data onto the telephony channel. The telephony channel then carries
the data traffic to the eventual destination. At the receiving end (in this case, the central station)
the telephony signal is transformed back to RS-232 format which can then be used by DTEs (Data
Terminal Equipment) such as comp uters and data processing equipment.
Therefore, the Telesto modem at a remote site must be paired with a corresponding modem at the
central site. Both of these units perform the same function - they transform the local data stream to
a form suitable for transmission on the leased line telephone network. Because data flow can occur
in both directions, i.e., to/from a remote site, the Telesto private wire modem is a full-duplex device.
This allows seis mic data to be sent continuously to the central data acquisition site while also
providing a return path for retransmission requests from the central site.
Both the remote site Telesto modem and its counterpart at the central site perform error detection
and correction which may have been caused by noise on the telephone channel. This function is
performed transparently, i.e., neither the Europa digitiser nor the central site data acquisition
equipment have knowledge of this real-time error correction.
The Telesto modem has been designed to require no “handshaking” between itself and the data
device connected to it, e.g., Europa digitiser. Only 3 signal lines are necessary to transmit/receive
data over the leased-line telephone network with the Telesto; thes e are Tx (Transmit), Rx (Receive)
and GND (Ground). Data to be transmitted is simply placed on the Tx line while data to be received
is obtained by monitoring the Rx line; GND serves as an electrical return path.
Power Conversion (Optional)
Because the available power at the remote site is 24 VDC, the Telesto Private Wire Modem
converts this voltage to a 12 VDC level required by the Europa digitiser. As well the Telesto’s
internal electronics require different voltage levels. The power conversion is accomplished inside
the Telesto with the use of 3 DC/DC converters. These solid state devices provide 15 VDC, 12 VDC
and 5 VDC. The 12 VDC is made available to the Europa Digitizer via a MIL connector on the front
panel of the Telesto enclosure.
Technical Description
Telesto Private Wire Modem 10