# Configuring clock slaves and standalone boards

Any board connected to the CT bus that is not the primary or secondary clock master must be configured as a clock slave. Each clock slave derives its primary timing reference from A_CLOCK or B_CLOCK (whichever is driven by the primary clock master).

If you have set up a secondary clock master, when the primary clock master stops driving its CT bus clock, the clock slaves can get their clocking information from the secondary clock master.

Use the following keywords to configure clock slaves:

Keyword | Description
--- | ---
Clocking.HBus.ClockMode | Specifies the CT bus clock that the board drives. For a clock slave, set to SLAVE to indicate that the board does not drive any CT bus clock.
Clocking.HBus.ClockSource | Specifies the primary timing reference for the board. For each slave, set to the CT bus clock driven by the primary master: A_CLOCK or B_CLOCK.
Clocking.HBus.AutoFallBack | Enables or disables clock fallback on the board. If you have set up a secondary clock master, set to YES for each slave. Otherwise, set to NO.
Clocking.HBus.FallBackClockSource | Specifies the fallback timing reference for the board, to use if the primary timing reference fails. If you have set up a secondary clock master, set to the timing reference driven by the secondary clock master. Once a slave switches to the secondary clock, it continues to use the clock until reset by an application.

## Configuring standalone boards

Configure a board in standalone mode so that the board references its own timing information, set Clocking.HBus.ClockMode to STANDALONE.

In this mode, the board is not able to make connections to the CT bus.

With some board models, specifying standalone mode can cause certain default switch connections to be made on the board to route incoming information from the trunk to DSP resources. The SwitchConnections and SwitchConnectMode keywords control this behavior. Refer to the board documentation for more information.