SENA PS810 - Manual (Page 66)

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 Automatic release modem connection
If Automatic release modem connection is set as Enable, modem connection will be closed by Pro
Series if all TCP connections are closed. If this option is set as Disable, modem connection will not be
closed by Pro Series even if all TCP connections are closed. Please note that actual phone line
connection will be closed if one of modems closes connection. That is, this option can be used for Pro
Series to allow disconnection of a modem connection by itself when all TCP connections are closed.
If user wants to use dial-out function, he should set DCD behavior as None because he must be able
to access modem connected to a serial port to send dial out command to the modem first.
Figure 4-18 Modem configuration