# Clocking.HBus.AutoFallBack

Enables clock fallback on the board.

For more information about setting up CT bus clocking and about the rules and restrictions that apply to setting up clocking with CG 6565C boards, refer to Configuring board clocking.

#### Syntax

Clocking.HBus.AutoFallBack = mode

#### Access

Read/Write

#### Type

String

#### Default

NO

#### Allowed values

YES | NO

#### Example

Clocking.HBus.AutoFallBack = YES

#### Details

Set to YES to specify that the board automatically switches to an alternative timing reference (specified with the Clocking.HBus.FallBackClockSource keyword) when the first timing reference (specified with the Clocking.HBus.ClockSource keyword) fails.

This keyword applies for all modes specified by the Clocking.HBus.ClockMode keyword.

The physical timing references specified with the Clocking.HBus.ClockSource and Clocking.HBus.FallBackClockSource keywords must be present and not in an ALARM state when the CG 6565C board's clocking is set up.

Specifying NO indicates that the system does not fall back to a backup timing reference.

If the board is configured as the primary master or in standalone mode, Clocking.HBus.FallBackClockSource enables the board to switch to the fallback timing reference when the first source goes into an ALARM state.

Note: Use the swish command queryBoardClck to determine what timing reference the board is actively using.

In addition:

- If the primary clock master's first timing reference fails and then returns, the primary master's timing reference (and consequently the timing reference for any clock slaves) tries to switch back to the first source.

- If the primary clock master's first timing reference and fallback timing reference fail, the secondary clock master begins to drive the CT bus clock for all clock slaves. If either of the primary clock master's timing references then recover, the CT bus does not switch back to either of these sources. The secondary master continues to drive the CT bus clock until directed otherwise.

- If the board is configured as the primary clock master and both timing references fail, the board reconfigures itself to become a slave to the secondary H.100/H.110 timing reference.

- If the board is configured in standalone mode and both the first timing reference and fallback timing references fail, the board automatically switches to OSC.

#### See also

Clocking.HBus.FallBackNetwork