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INSTALLATION
PMC-100
APPLICATION
Primary Power
Connection
2-26
At each CSU site:
• Connect the modem to the DataComm 551 by means of the 25-pin
EIA/TIA-232-E male Supervisory port connector on the DataComm 551
rear panel, as shown in the appropriate figure. The interface cable
must be terminated on the modem end in a DB25P connector and on the
DataComm 551 end in a DB25S connector. The DataComm 551 requires
that the signals be connected to the pins as shown. For the modem, en-
able Auto Answer (for unattended operation), disable terminal com-
mands (to prevent the modem from responding to commands intended
for the CSU), and select XOFF/XON flow control (if applicable, to pre-
vent losing data when the modem is operating at a slower speed than
the CSU).
In a PMC-100 application, such as illustrated in Figures 1-3 through 1-5,
the Supervisory terminal can be used to access all CSUs in the network.
The PMC-100s at the hub site allow direct access to their CSUs, as well as
access to the other sites' CSUs via in-band communication. The modem at
each the other sites allows access to its CSU via out-of-band communica-
tion.
a. Be sure to select a unique address number and en-
able PMC-100 operation for each CSU in the net-
work.
b. When
PMC-100
DataComm 551, its Supervisory port is disabled. Su-
pervisory terminal communications are handled on
the RS-485 bus interconnecting the units.
Refer to the PMC-100 manual for additional PMC-100 installation instruc-
tions.
After the above connections have been made, the options selected, and the
DataComm 551s installed, refer to the following instructions on connect-
ing primary power to the system. The outlet used to provide ac power,
where applicable, should not be under switch control. The DataComm 551
should be powered by the same ac source as the customer equipment inter-
faced with it to prevent large circulating currents caused by differences
in ground potential. If it is not possible to determine whether the customer
equipment is powered by the same ac source, it should be verified that a
potential difference of less than 0.25 V rms exists between the grounding
circuits of the respective outlets.
NOTES
Operation
is
selected
for
a
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