> 3.4 | Wake on ring

> If the operating system is in standby mode and the module has not been switched off, incoming calls and real time clock alarms should wake up the operating system (wake on ring). This feature belongs to the ACPI power management mechanisms that are not properly implemented on all PC systems. It is independent of the multiplexer driver. When the ring signal toggles on the serial interface like on incoming calls and real time clock alarms, this should wake up the operating system, if the PC has been properly configured. On some systems not the ring signal but data transferred to the PC (the “RING” or “CALA” messages from the module) wake up the operating system. To avoid loss of data the multiplexer driver switches on the hardware flow control on the module. This means that the module cannot send data to the PC, if the operating system is in standby mode and therefore the serial interface is blocked by the hardware flow control. As a consequence the operating system does not wake up, if the system ignores the ring signal, because the module cannot send the “RING” or “CALA” messages to the PC.