# Configuring the H.100 or H.110 bus clock

If the boards are connected to each other on the H.100 or H.110 bus, set up a bus clock to synchronize communications between the boards connected to the bus. In addition, to provide redundant and fault-tolerant clocking between devices on the bus, configure alternative (fallback) clock sources to provide the clock signal if the primary source fails.

To configure the bus clock for a system:

- Configure a board to act as clock master, driving the bus clock.

- (Optional) Configure another board to act as secondary clock master, driving the clock if the primary clock master fails.

- Configure primary and secondary timing references for each clock master board. The timing reference for a board is an external signal from which it can derive a clock pulse.

- Configure all other boards as clock slaves, so they synchronize to the clock master signal.

Refer to CT bus clocking overview for more information. For specifics on setting up clocking for the boards, refer to the board documentation.

## Clock Management EMC

The NMS OAM service provides H.100 and H.110 bus clock management services to boards in a chassis that is connected through the bus. This functionality is provided in the Clock Management EMC.

When the boards in a system are started, the Clock Management EMC:

- Configures the clock on each board as specified in the NMS OAM database.

- Ensures that the bus clock master board (the board driving the clock) is running before setting the clocks on the slave boards.

Refer to the NMS OAM Service Developer's Reference Manual for more information about the Clock Management EMC.