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P300H P300 Series Modem Installation and Operating Handbook Page 178
Eurocom D/1 interface `G` operation
The Eurocom `G` interface uses transformer coupled differential combined clock and data signal which
is diphase coded. The amplitude is ±1.0V (ie 2.0 V peak to peak). The lines are of 130
impedance, and
the centre tap of the line coupling transformers may either be grounded, or left floating.
The Eurocom `G` interface will operate at either 16kbps of 32kbps only, NO OTHER DATA RATES
are supported. The modem will generate a configuration error if configured for data rates outside the
range 16-32kbps, but note that only 16kbps & 32kbps are valid rates for operation of the Eurocom
interface. For example configuring the modem for 20kbps will NOT cause an error, but the Eurocom
interface will not function correctly at this rate.
Min
Req
Signal Description centre tap of
25 pin Link to ground
transformer
AB
DATA CIRCUIT TOWARDS MODEM (TX)
Clock/Data In 24 11 LK 3 *
DATA CIRCUIT FROM MODEM (RX)
Clock/Data Out 23 10 LK 6 *
COMMON LINES
Ground to Activate Eurocom `G` at 16kbps 20 n/a
Ground to Activate Eurocom `G` at 32kbps 14 AND 20 n/a
Do Not Connect 12 n/a
Signal Ground 2, 7, 13, 15, 22, 25 n/a
Shield/Protective ground 1n/a
* Links
All links settings are:
Centre tap grounded: 1-2 (link `up` with the PCB legend the right way up)
Centre tap floating 2-3 (link `down` with the PCB legend the right way up)
The typical configuration would normally be to ground the outputs, and leave the inputs floating ie:
Link 6 in pos 1-2 (up), and link 3 in pos 2-3 (down)
This provides protection by ensuring the signal levels remain close to ground potential (as might happen
if both inputs and outputs were floating), but avoid any ground currents between distant locations (as might
happen if both inputs and outputs were grounded).