Advantech ADAM-5511 Manual page 198

modem_handup
Syntax:
void modem_handup(void)
Description:
Sets the modem to hand up the telephone. The command has the same
effect as sending the ASCII command "atho" to the modem.
Parameter Description
None.
Return value:
None.
Example:
void main()
{
//close phone
modem_handup();
}
Remarks:
None.