ADT7463
FUNCTIONAL DESCRIPTION
INTERNAL REGISTERS OF THE ADT7463
General Description
A brief description of the ADT7463’s principal internal registers
is given below. More detailed information on the function of
each register is given in Tables IV to XLII.
The ADT7463 is a complete systems monitor and multiple fan
controller for any system requiring monitoring and cooling. The
device communicates with the system via a serial system
management bus. The serial bus controller has an optional
address line for device selection (Pin 14), a serial data line
for reading and writing addresses and data (Pin 1), and an input
line for the serial clock (Pin 2). All control and programming
functions of the ADT7463 are performed over the serial bus. In
addition, two of the pins can be reconfigured as an SMBALERT
output to indicate out-of-limit conditions.
Configuration Registers
The configuration registers provide control and configuration of
the ADT7463, including alternate pinout functionality.
Address Pointer Register
This register contains the address that selects one of the other
internal registers. When writing to the ADT7463, the first byte
of data is always a register address, which is written to the
address pointer register.
Measurement Inputs
Status Registers
The device has six measurement inputs, four for voltage and
two for temperature. It can also measure its own supply voltage
and can measure ambient temperature with its on-chip tempera-
ture sensor.
These registers provide the status of each limit comparison and
are used to signal out-of-limit conditions on the temperature,
voltage, or fan speed channels. If Pin 10 or Pin 22 is con-
figured as SMBALERT, then this pin asserts low whenever a
status bit gets set.
Pins 20 through 23 are analog inputs with on-chip attenuators,
configured to monitor 5 V, 12 V, 2.5 V, and the processor core
voltage (2.25 V input), respectively.
Interrupt Mask Registers
These registers allow each interrupt status event to be masked
when Pin 10 or Pin 22 is configured as an SMBALERT output.
Power is supplied to the chip via Pin 4, and the system also
monitors VCC through this pin. In PCs, this pin is normally
connected to a 3.3 V standby supply. This pin can, however, be
connected to a 5 V supply and monitor it without overranging.
VID Register
The status of the VID0 to VID5 pins of the processor can read
from this register. VID code changes can also generate
SMBALERT interrupts.
Remote temperature sensing is provided by the D1� and D2�
inputs, to which diode-connected, external temperature-sensing
transistors, such as a 2N3904 or CPU thermal diode, may be
connected.
Value and Limit Registers
The results of analog voltage inputs, temperature, and fan speed
measurements are stored in these registers, along with their
limit values.
The ADC also accepts input from an on-chip band gap tem-
perature sensor that monitors system ambient temperature.
Offset Registers
These registers allow each temperature channel reading to be
offset by a twos complement value written to these registers.
Sequential Measurement
When the ADT7463 monitoring sequence is started, it cycles
sequentially through the measurement of analog inputs and the
temperature sensors. Measured values from these inputs are
stored in value registers. These can be read out over the serial
bus or can be compared with programmed limits stored in the
limit registers. The results of out-of-limit comparisons are stored
in the status registers, which can be read over the serial bus to
flag out-of-limit conditions.
TMIN Registers
These registers program the starting temperature for each fan
under automatic fan speed control.
TRANGE Registers
These registers program the temperature-to-fan speed control
slope in automatic fan speed control mode for each PWM output.
Processor Voltage ID
Operating Point Registers
Five digital inputs (VID0 to VID5—Pins 5 to 8, 19, and 21) read
the processor voltage ID code and store it in the VID register,
from which it can be read out by the management system over
the serial bus. The VID code monitoring function is compatible
with both VRM9.x and future VRM10 solutions. Additionally,
an SMBALERT can be generated to flag a change in VID code.
These registers define the target operating temperatures for each
thermal zone when running under dynamic TMIN control. This
function allows the cooling solution to adjust dynamically in
response to measured temperature and system performance.
Enhance Acoustics Registers
These registers allow each PWM output controlling fan to be
tweaked to enhance the system’s acoustics.
ADT7463 Address Selection
Pin 13 is the dual-function PWM3/ADDRESS ENABLE pin.
If Pin 13 is pulled low on power-up, the ADT7463 reads the
state of Pin 14 (TACH4/ADDRESS SELECT/ THERM pin) to
determine the ADT7463’s slave address. If Pin 13 is high on
power-up, then the ADT7463 defaults to the SMBus slave
Address 0x2E. This function is described in more detail later.
Rev. 4 | Page 6 of 52 | www.onsemi.com
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