# Clocking.HBus.AutoFallBack

Enables or disables clock fallback on the board. This keyword specifies whether or not the board automatically switches to a secondary timing reference if its primary timing reference fails.

For information about setting up CT bus clocking, and rules and restrictions for configuring CT bus clocking, refer to Configuring board clocking.

#### Syntax

Clocking.HBus.AutoFallBack = argument

#### Access

Read/Write

#### Type

String

#### Default

NO

#### Allowed values

YES | NO

#### Example

Clocking.HBus.AutoFallBack = NO

#### Details

The primary timing reference is specified by the Clocking.HBus.ClockSource keyword. The secondary timing reference is specified by the Clocking.HBus.FallbackClockSource keyword.

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

For more information about clock fallback, refer to the NMS OAM System User's Manual.

#### See also

Clocking.HBus.ClockMode, Clocking.HBus.NetRefSource, Clocking.HBus.NetRef2Source