Fan Control Device with High Frequency PWM and Temperature Monitors
Datasheet
4. [5C-5Eh] Set the fan spin-up delays.
5. [5C-5Eh] Match each PWM output with a corresponding thermal zone.
6. [67-69h] Set the zone temperature low limits.
7. [6A-6Ch] Set the zone temperature absolute limits.
8. [64-66h] Set the PWM minimum duty cycle.
9. [81h] Associate a Tachometer input to a PWM output Register
10. [90-93h] Select the TACH Mode of operation (Mode 1 or Mode 2)
11. [90-93h] Set the number of edges per tach reading
12. [90-93h] Set the ignore first 3 edges of tach input bit
13. [90-93h] Set the SLOW bit to 0b if tach reading should indicated slow fan event as FFFEh and 1b
if stalled fan event as FFFFh.
14. [94-96h] Set the TACH Reading Update rate
15. [94-96h] Set the tach reading guard time (Mode 2 Only)
16. [94-96h] Set the TACH reading logic for Opportunistic Mode (Mode 2 Only)
17. [94-96h] Set the SZEN bit, which determines if the PWM output will ramp to Off or jump to Off.
18. [40h] Set bit 0 (Start) to start monitoring.
19. [40h] Set bit 1 (Lock) to lock the limit and parameter registers (optional)
7.1.3
PWM Fan Speed Control
Note: The following description applies to PWM1, PWM2, and PWM3.
When describing the operation of the PWMs, the terms “Full on” and “100% duty cycle” means that
the PWM output will be high for 255 clocks and low for 1 clock (INVERT bit = 0). The exception to this
is during fan spin-up when the PWM pin will be forced high for the duration of the spin-up time.
7.1.3.1
Manual Fan Control Operating Mode (Test Mode)
When operating in Manual Fan Control Operating Mode, software controls the speed of the fans by
directly programming the PWM duty cycle. The operation of the fans can be monitored based on
reading the temperature and tachometer reading registers and/or by polling the interrupt status
registers. The EMC2300 offers the option of generating an interrupt indicated by the INT# signal located
on the PWM2 and TACH3 pins.
To control the PWM outputs in manual mode:
Write ‘111’ to bits[7:5] Zone/Mode, located in Registers 5Ch-5Eh: PWMx Configuration.
The speed of the fan is controlled by the duty cycle set for that PWM output. The duty cycle must
be programmed in Registers 30h-32h: Current PWM Duty
To monitor the fans:
Fans equipped with Tachometer outputs can be monitored via the TACHx input pins. See Section 7.1.4,
"Fan Speed Monitoring," on page 38.
If an out-of-limit condition occurs, the corresponding status bit will be set in the Interrupt Status
registers. Setting this status bit will generate an interrupt signal on the INT# pin (if enabled). Software
must handle the interrupt condition and modify the operation of the device accordingly. Software can
evaluate the operation of the Fan Control device through the Temperature and Fan Tachometer
Reading registers.
When in manual mode, the current PWM duty cycle registers can be written to adjust the speed of the
fans, when the start bit is set. These registers are not writable when the lock bit is set.
Revision 0.2 (06-14-06)
SMSC EMC2300
DATA3S0HEET
SMSC [ SMSC CORPORATION ]
