# Clocking.HBus.FallBackClockSource

Specifies the alternate clock reference to use when the master clock does not function properly.

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.FallBackClockSource = clock_source

#### Access

Read/Write

#### Type

String

#### Default

OSC

#### Allowed values

OSC | A_CLOCK | B_CLOCK

#### Example

Clocking.HBus.FallBackClockSource = OSC

#### Details

If the Clocking.HBus.AutoFallBack keyword is set to NO, this keyword is ignored.

For more information about clock fallback, refer to the Switching Service Developer's Reference Manual.

To support clock fallback on an AG board, refer to the NMS web site (www.nmscommunications.com) for application notes and other updates.