Mitsubishi Electric MELSEC iQ-R Series User Manual page 200

When the line connection is initiated from the target device, any of the registration, setting or connection
processing related to the line connection is not necessary.
Data communication is available when the 'Connection' (X12) turns ON after the completion of the C24
modem/TA initialization.
Page 191 Input/output signals used for line connection
For program example of the modem/TA for initialization, refer to the following section.
Page 187 Modem/TA initialization with a program
7 COMMUNICATIONS BY THE MODEM FUNCTION
198
7.4 Startup of the Modem Function