Sun Microsystems Blade 1500 Service, Diagnostics, And Troubleshooting Manual page 469

modulated outputs control the fan speeds by varying the output duty cycle from
33% to 100%. The speed of each fan is monitored from fan tachometer feedback and
adjusted appropriately.
There are two alarm outputs from ADM1031:
Programmable interrupt output, INT#
■
Emergency power-off output, THERM#
■
The signal from the temperature sensors is analyzed by the OpenBoot PROM which
instructs the ADM1031 to set an optimal fan speed for cooling. Should an overheat
condition occur, an interrupt is triggered to inform the Solaris software of the
situation.
If the temperature exceeds a programmed threshold value, the ADM1031 goes to an
alarm state and sends an emergency power-off interrupt directly to the M1535D+
I/O subsystem, powering off the Sun Blade 1500 workstation to prevent CPU
damage.
shows a block diagram of the cooling fan control system.
FIGURE C-7
TEMP_SENSE+
CPU TEMP_SENSE-
Thermal Diode
Cooling Fan Control Block Diagram
FIGURE C-7
Note – Though there are two system fans, only the front system fan provides
tachometer feedback to the ADM1031.
ADM1031
PWM1
SCL
TACH1
SDA
PWM2
TACH2
D0+
D0-
D1+
INT#
D1-
THERM#
Appendix C Functional Description
CPU Fan
System Fans
IChip2
M1535D+ EM_OFF pin
C-37