Multiple RPM-Based PWM Fan Controller for Five Fans
Datasheet
Bit 1 - DR_EXT_CLK - Enables the internal tachometer clock to be driven out on the CLK pin so that
multiple devices can be synced to the same source.
‘0’ (default) - The CLK pin acts as a clock input.
‘1’ - The CLK pin acts as a clock output and is a push-pull driver.
Bit 0 - USE_EXT_CLK - Enables the EMC2305 to use a clock present on the CLK pin as the
tachometer clock. If the DR_EXT_CLK bit is set, then this bit is ignored and the device will use the
internal oscillator.
‘0’ (default) - The EMC2305 will use its internal oscillator for all Tachometer measurements.
‘1’ - The EMC2305 will use the oscillator presented on the CLK pin for all Tachometer
measurements.
5.3
Fan Status Registers
Table 5.3 Fan Status Registers
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
DRIVE_
FAIL
FAN_
SPIN
FAN_
STALL
24h
R-C
Fan Status
WATCH
-
-
-
-
00h
Fan Stall
Status
FAN5_
STALL
FAN4_
STALL
FAN3_
STALL
FAN2_
STALL
FAN1_
STALL
25h
26h
27h
R-C
R-C
R-C
-
-
-
-
-
-
-
-
-
00h
00h
00h
Fan Spin
Status
FAN5_
SPIN
FAN4_
SPIN
FAN3_
SPIN
FAN2_
SPIN
FAN1_
SPIN
Fan Drive
Fail Status
DRIVE_
FAIL5
DRIVE_
FAIL4
DRIVE_
FAIL3
DRIVE_
FAIL2
DRIVE_
FAIL1
The Fan Status registers contain the status bits associated with each fan driver.
5.3.1
Fan Status - 24h
The Fan Status register indicates that one or more of the fan drivers has stalled or failed or that the
Watchdog Timer has expired (see Section 4.8).
Bit 7 - WATCH - Indicates that the Watchdog Timer has expired. When set, each fan is driven to 100%
duty cycle and will remain at 100% duty cycle until they are programmed. This bit is cleared when it
is read.
Bit 2 - DRIVE_FAIL - Indicates that one or more fan drivers cannot meet the programmed fan speed
at maximum PWM duty cycle. This bit is set when any bit in the Fan Drive Fail Status register is set
and cleared when all bits in the Fan Drive Fail Status register are cleared.
Bit 1 - FAN_SPIN - Indicates that one or more fan drivers cannot spin up. This bit is set when any bit
in the Fan Spin Status register is set and cleared when all of the bits in the Fan Spin Status register
are cleared.
Bit 0 - FAN_STALL - Indicates that one or more fan drivers have stalled. This bit is set when any bit
in the Fan Stall Status register is set and cleared when all of the bits in the Fan Stall Status register
are cleared.
5.3.2
Fan Stall Status - 25h
The Fan Stall Status register indicates which fan driver has detected a stalled condition (see
Section 4.4.1). All bits are cleared upon a read if the error condition has been removed.
Revision 1.1 (10-12-09)
SMSC EMC2305
DATA3S2HEET
SMSC [ SMSC CORPORATION ]
