adt7476a Analog Devices, Inc., adt7476a Datasheet - Page 26

• Manufacturer Part Number: adt7476a
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

ADT7476A
Bit 4 (FAN3) = 1, masks SMBALERT for Fan 3.
Bit 3 (FAN2) = 1, masks SMBALERT for Fan 2.
Bit 2 (FAN1) = 1, masks SMBALERT for Fan 1.
Bit 1 (OVT) = 1, masks SMBALERT for overtemperature
(exceeding THERM temperature limits).
Bit 0 (12V/VC) = 1, masks SMBALERT for 12 V channel or
for a VID code change, depending on the function used.
Enabling the SMBALERT Interrupt Output
The SMBALERT interrupt function is disabled by default.
Pin 10 or Pin 14 can be reconfigured as an SMBALERT
output to signal out-of-limit conditions.
Table 15. Configuring Pin 10 as SMBALERT Output
Register
Configuration Register 3 (0x78)
Assigning THERM Functionality to a Pin
Pin 14 on the ADT7476A has four possible functions:
SMBALERT , THERM , GPIO6, and TACH4. The user
chooses the required functionality by setting Bit 0 and Bit 1
of Configuration Register 4 (0x7D).
If THERM is enabled on Bit 1, Configuration Register 3 (0x78):
•
•
If THERM is not enabled:
•
•
Table 16. Configuring Pin 14
Bit 0
0
0
1
1
THERM as an Input
When THERM is configured as an input, the user can time
assertions on the THERM pin. This can be useful for connecting
to the PROCHOT output of a CPU to gauge system performance.
Pin 22 becomes THERM .
If Pin 14 is configured as THERM on Bit 0 and Bit 1 of Con-
figuration Register 4 (0x7D), THERM is enabled on this pin.
Pin 22 becomes a 2.5 V measurement input.
If Pin 14 is configured as THERM , then THERM is
disabled on this pin.
Bit 1
0
1
0
1
Bit Setting
[1] Pin 10 = SMBALERT
[0] Pin 10 = PWM2
Function
TACH4
THERM
SMBALERT
GPIO6
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When the THERM pin is driven low externally, the user can
also set up the ADT7476A to run the fans at 100%. The fans run
at 100% for the duration of time that the THERM pin is pulled low.
This is done by setting the BOOST bit (Bit 2) in Configuration
Register 3 (0x78) to 1. This works only if the fan is already running,
for example, in manual mode, when the current duty cycle is above
0x00, or in automatic mode when the temperature is above T
If the temperature is below T
mode is set to 0x00, pulling the THERM low externally has no
effect. See Figure 31 for more information.
THERM TIMER
The ADT7476A has an internal timer to measure THERM
assertion time. For example, the THERM input can be
connected to the PROCHOT output of a Pentium 4 CPU to
measure system performance. The THERM input can also be
connected to the output of a trip-point temperature sensor.
The timer is started on the assertion of the ADT7476A’s THERM
input and stopped when THERM is de-asserted. The timer counts
THERM times cumulatively; that is, the timer resumes counting
on the next THERM assertion. The THERM timer continues to
accumulate THERM assertion times until the timer is read
(where it is cleared), or until it reaches full scale. If the counter
reaches full scale, it stops at that reading until cleared.
The 8-bit THERM timer status register (0x79) is designed so
that Bit 0 is set to 1 on the first THERM assertion. Once the
cumulative THERM assertion time has exceeded 45.52 ms, Bit 1
of the THERM timer is set and Bit 0 now becomes the LSB of
the timer with a resolution of 22.76 ms (see Figure 32).
T
THERM
THERM ASSERTED TO LOW AS AN INPUT:
FANS DO NOT GO TO 100% BECAUSE
TEMPERATURE IS BELOW T
MIN
Figure 31. Asserting THERM Low as an Input
in Automatic Fan Speed Control Mode
MIN
.
THERM ASSERTED TO LOW AS AN INPUT:
FANS DO NOT GO TO 100% BECAUSE
TEMPERATURE IS ABOVE T
ARE ALREADY RUNNING.
MIN
or if the duty cycle in manual
MIN
AND FANS
MIN
.