Rockwell Automation 1770-KF3 DH-485 Communication Interface User Manual - Manual (Page 43)

Communicating with the KF3
Chapter 4
4Ć10
This handshaking is necessary to guarantee access to the phone line. If the
handshaking protocol is defeated by improper selection of modem options
or by jumpers at the connectors, the modem may still answer a call. But
if the connection is lost, the modem will not hang up. It will then be
impossible for the remote node to reestablish the connection because it will
get a busy signal.