Sun Microsystems 6.0005E+11 manual ConsoleBus, Clocks, Reset logic

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6.2.1 ConsoleBus

The ConsoleBus provides system boards access to global system control and status as well as to the keyboard, mouse, and serial ports. In addition, there is a NVRAM/TOD chip that maintains the date and time and 8 Kbytes worth of data when the power to the system is shut off.

The state of physical hardware conditions is maintained in registers on the clock board. Each of these registers has inputs generated from other subsystems on the clock board, from other boards, or from the power supplies in the system. Some clock board registers are reserved for controlling various states of the machine.

The ConsoleBus also provides a serial port interface and a keyboard/mouse interface. The primary purpose of the serial port interface is to provide POST messages during power-on. The serial port can be used as a console for systems without a keyboard and display, and for standard serial peripheral hook-us such as modems and printers.

6.2.2 Clocks

The clock subsystem generates the clocks for the entire system. The base clock is synthesized and then divided into various frequencies. The base clocks are then “fanned-out” and driven to the centerplane by an array of driver chips.

Two processor clocks and one system clock go to each of the board slots on the centerplane.

6.2.3 Reset logic

The reset logic consists of four subcircuits for controlling the system reset and error state:

•Manual reset

•System reset

•XIR

•System error

6-4 Ultra Enterprise 6000/5000/4000 Systems Manual—November 1996