Advantech ADAM-5511 Manual page 200

modem_command_state
Syntax:
void modem_command_state(void)
Description:
Sets modem to command mode. In other words, this causes the modem
to escape from data mode to command mode. The modem will delay at
least 3 seconds before switching back to command mode. This
command has the same effect as sending the ASCII command "+++" to
the modem.
Parameter Description
None.
Return value:
None.
Example:
void main()
{
//receiving data from modem, so modem is in transfer data mode
modem_command_state();
//now, you can send an AT command string to modem
}
Remarks:
None.