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ADM1025A Datasheet(PDF) 9 Page - ON Semiconductor
ONSEMI [ON Semiconductor]
ADM1025A Datasheet(HTML) 9 Page - ON Semiconductor
/ 21 page
Preliminary Technical Data
Rev. P5 | Page 9 of 21| www.onsemi.com
The ADM1025/ADM1025A is a complete system hardware
monitor for microprocessor-based systems. The device
communicates with the system via a serial System Management
Bus. The serial bus controller has a hardwired address line for
device selection (Pin 16), 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 ADM1025/ADM1025A are performed over the serial bus.
The device has six measurement inputs, five for voltage and one
for temperature. It can also measure its own supply voltage and
can measure ambient temperature with its on-chip temperature
Pins 11 through 15 are analog inputs with on-chip attenuators
configured to monitor 12 V, 5 V, 3.3 V, 2.5 V, and the processor
core voltage, respectively. Pin 11 may alternatively be
programmed as a digital input for Bit 4 of the processor voltage
Power is supplied to the chip via Pin 4, and the system also
monitors the voltage on this pin.
Remote temperature sensing is provided by the D+ and D−
inputs, to which a diode-connected, external temperature-
sensing transistor may be connected.
An on-chip band gap temperature sensor monitors system
When the ADM1025/ADM1025A 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
PROCESSOR VOLTAGE ID
Five digital inputs (VID4 to VID0—Pins 5 to 8 and 11) read the
processor voltage ID code and store it in the VID registers, from
which it can be read out by the management system over the
serial bus. If Pin 11 is configured as a 12 V analog input (power-
up default), the VID4 bit in the VID4 register will default to 0.
The VID pins have internal 100 kΩ pull-up resistors (ADM1025
Pin 16 is a programmable digital I/O pin. After power-up, at the
first sign of SMBus activity, it is sampled to set the lowest two
bits of the serial bus address. During board-level, NAND tree
connectivity testing, this pin functions as the output of the
NAND tree. During normal operation, Pin 16 may be
programmed as a reset output to provide a low going 20 ms
reset pulse when enabled, or it may be programmed as an
interrupt output for out-of-limit temperature and/or voltage
events. These functions are described in more detail later.
INTERNAL REGISTERS OF THE
A brief description of the ADM1025/ADM1025A’s principal
internal registers is given below. More detailed information on
the function of each register is given in Table 8 to Table 18.
Provides control and configuration.
Address Pointer Register:
This register contains the address
that selects one of the other internal registers. When writing to
the ADM1025/ADM1025A, the first byte of data is always a
register address, which is written to the Address Pointer
Two registers to provide status of each limit
The status of the VID0 to VID4 pins of the
processor can read from these registers.
Value and Limit Registers:
The results of analog voltage inputs
and temperature measurements are stored in these registers,
along with their limit values.
Allows either an internal or external
temperature channel reading to be offset by a twos complement
value written to this register.
SERIAL BUS INTERFACE
Control of the ADM1025/ADM1025A is carried out via the
serial bus. The ADM1025/ADM1025A is connected to this bus
as a slave device, under the control of a master device or master
The ADM1025/ADM1025A has a 7-bit serial bus address.
When the device is powered up, it will do so with a default
serial bus address. The five MSBs of the address are set to
01011; the two LSBs are determined by the logical states of Pin
16 at power-up. This is a three-state input that can be grounded,
connected to V
, or left open-circuit to give three different
Table 4. Address Selection
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