Sun Microsystems 6.0005E+11 - Manual (Page 128)

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