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Appendix B Components B-17
B.10 Clock Control Unit
A clock control unit (CLKU: formal abbreviation is CLKU_B) is mounted only in the M9000
server, and it supplies clock signals to a CMU and crossbar unit (XBU). Furthermore, in the
M9000 server with the expansion cabinet, both CLKUs in the base cabinet and expansion
cabinet are connected to enable each to supply clock signals to the other cabinet.
In the M8000, two LSI chips for clock signals instead of the CLKU are mounted on the
backplane.
FIGURE B-10 shows the CLKU_B.
FIGURE B-10 Clock Control Unit (CLKU_B)
The CLKU has the following characteristics.
■ Only cold replacement is available for CLKU_B.
■ A dedicated LSI chip is used for clock control.
■ CMU and XBU are supplied with the standard clocks, respectively.
■ The CLKU has a label bearing the printed component number and manufacture's serial
number.
B.11 XSCF Unit
The XSCF unit (XSCFU: eXtended System Control Facility unit) controls the system.