# DCM Modes

The following DCM Modes are available:

| Name              | Purpose                                                                                                                                  |
|-------------------|------------------------------------------------------------------------------------------------------------------------------------------|
| BusShift          | Synchronize SubDevices to MainDevice timer (Default)                                                                                     |
| MasterShift       | Synchronize MainDevice timer to SubDevice. Feasibility<br/>depending on target HW and SW.                                                |
| LinkLayerRefClock | Bus Shift using Link Layer clock. Special HW needed.                                                                                     |
| MasterRefClock    | Bus Shift excluding reference clock controlling.<br/>Lowers CPU usages, but very high timer accuracy needed.                             |
| DCX               | Synchronization of two or more EtherCAT® segments by a<br/>bridge device. Only available with Feature Pack<br/>External Synchronization. |

The Distributed Clocks MainDevice Synchronization (DCM) in Bus Shift mode adjusts the bus time register of the DC reference clock. All DC SubDevices converge to this time.
This mode is useful to synchronize multiple EtherCAT® networks or if it is not possible to adjust the timing of the MainDevice.

#### SEE ALSO
[`emDcmConfigure()`](dcm_api.html.md#_CPPv414emDcmConfigure10EC_T_DWORDPK15EC_T_DCM_CONFIG10EC_T_DWORD)