ADM1024
General Description
Processor Voltage ID
The ADM1024 is a complete system hardware monitor for
microprocessor−based systems. The device communicates
with the system via a serial SMBus. The serial bus controller
has a hardwired address line for device selection (Pin 1), a
serial data line for reading and writing addresses and data
(SDA, Pin 14), and an input line for the serial clock (Pin 3),
and an input line for the serial clock (Pin 4). All control and
programming functions of the ADM1024 are performed over
the serial bus.
Measurement Inputs
Five digital inputs (VID4 to VID0—Pins 20 to 24) read
the processor voltage ID code. These inputs can also be
reconfigured as interrupt inputs.
The VID pins have internal 100 kW pullup resistors.
Chassis Intrusion
A chassis intrusion input (Pin 7) is provided to detect
unauthorized tampering with the equipment.
RESET
Programmability of the measurement inputs makes the
ADM1024 extremely flexible and versatile. The device has
a 10−bit ADC and nine measurement input pins that can be
configured in different ways.
Pins 5 and 6 can be programmed as general−purpose
analog inputs with a range of 0 V to 2.5 V, or as digital inputs
to monitor the speed of fans with digital tachometer outputs.
The fan inputs can be programmed to accommodate fans
with different speeds and different numbers of pulses per
revolution from their tachometer outputs.
Pins 13 and 14 are dedicated temperature inputs and may
be connected to the cathode and anode of an external
temperature sensing diode.
Pins 15, 16, and 19 are dedicated analog inputs with
on−chip attenuators, configured to monitor 12 V, 5.0 V, and
the processor core voltage, respectively.
Pins 17 and 18 may be configured as analog inputs with
on−chip attenuators to monitor a second processor core voltage
and a 2.5 V supply, or they may be configured as a temperature
input and connected to a second temperature−sensing diode.
The ADC also accepts input from an on−chip band gap
temperature sensor that monitors system−ambient temperature.
Finally, the ADM1024 monitors the supply from which it
is powered, so there is no need for a separate 3.3 V analog
input if the chip V
CC
is 3.3 V. The range of this V
CC
measurement can be configured for either a 3.3 V or 5.0 V
V
CC
by Bit 3 of the Channel Mode Register.
Sequential Measurement
A RESET input/output (Pin 12) is provided. Pulling this
pin low will reset all ADM1024 internal registers to default
values. The ADM1024 can also be programmed to give a
low going 45 ms reset pulse at this pin.
Analog Output
The ADM1024 contains an on−chip, 8−bit DAC with an
output range of 0 V to 2.5 V (Pin 11). This is typically used
to implement a temperature−controlled fan by controlling
the speed of a fan dependent upon the temperature measured
by the on−chip temperature sensor.
Testing of board level connectivity is simplified by
providing a NAND tree test function. The AOUT (Pin 11)
also doubles as a NAND test input, while Pin 1 doubles as
a NAND tree output.
Internal Registers of the ADM1024
When the ADM1024 monitoring sequence is started, it
cycles sequentially through the measurement of analog
inputs and the temperature sensor, while at the same time the
fan speed inputs are independently monitored. 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 Interrupt
Status Registers, and will generate an interrupt on the INT
line (Pin 10).
Any or all of the Interrupt Status Bits can be masked by
appropriate programming of the Interrupt Mask Register.
A brief description of the ADM1024’s principal internal
registers follows. More detailed information on the function
of each register is given in Table 6 to Table 19:
♦
Configuration Registers: Provide control and
configuration.
♦
Channel Mode Register: Stores the data for the
operating modes of the input channels.
♦
Address Pointer Register: This register contains the
address that selects one of the other internal
registers. When writing to the ADM1024, the first
byte of data is always a register address, which is
written to the Address Pointer Register.
♦
Interrupt (INT) Status Registers: Two registers to
provide status of each interrupt event. These registers
are also mirrored at addresses 4Ch and 4Dh.
♦
Interrupt (INT) Mask Registers: Allow masking of
individual interrupt sources.
♦
Temperature Configuration Register: The
configuration of the temperature interrupt is
controlled by the lower three bits of this register.
♦
VID/Fan Divisor Register: The status of the VID0 to
VID4 pins of the processor can be written to and
read from these registers. Divisor values for fan
speed measurement are also stored in this register.
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