ADTRAN DSU III AR User Manual page 63

Chapter 6. Configuring DTE Options
The E C option is normally used in modem tail circuit
XTERNAL LOCK
applications. See Appendix E, DSU to DSU Tail Circuit on page E-1
for information about the DSU to modem interconnect diagram for
this application.
The E C option is also recommended when the
XTERNAL LOCK
EIA-232 connector is used for 56 kbps and 64 kbps applications. A
special DSU cable diagram for this application is shown in
Appendix D, EIA-232 Connector on page D-1. Using this option and
special cable eliminates data errors caused by excessive delays in
the DTE transmit clock receiver and transmit data driver.
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