PRELIMINARY TECHNICAL DATA ADM1026
–7–
REV. PrL
PRELIMINARY
TECHNICAL
DATA
FUNCTIONAL DESCRIPTION
GENERAL DESCRIPTION
The ADM1026 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 (ADD, pin 15), a serial data line for reading and
writing addresses and data (SDA, pin 14), and an input line
for the serial clock (SCL, pin 13). All control and pro-
gramming functions of the ADM1026 are performed over
the serial bus.
MEASUREMENT INPUTS
Programmability of the analog and digital measurement
inputs makes the ADM1026 extremely flexible and versa-
tile. The device has an 8 bit A to D converter, and 17 ana-
log measurement input pins that can be configured in
different ways.
Pins 25 and 26 are dedicated temperature inputs and may
be connected to the cathode and anode of a remote tem-
perature-sensing diode.
Pins 27 and 28 may be configured as a temperature input
and connected to a second temperature-sensing diode, or
they may be re-configured as analog inputs with a range of
0 to +2.5V.
Pins 29 to 33 are dedicated analog inputs with on-chip at-
tenuators, configured to monitor V
BAT
, +5V, -12V, +12V,
and the processor core voltage V
CCP
, respectively.
Pins 34 to 41 are general-purpose analog inputs with a
range of 0 to +2.5V or 0 to +3V. These are mainly in-
tended for monitoring SCSI termination voltages, but may
be used for other purposes.
The ADC also accepts input from an on-chip bandgap tem-
perature sensor that monitors system ambient temperature.
Finally, the ADM1026 monitors the supplies from which it
is powered, 3.3VMAIN and 3.3VSTBY, so there is no need
for separate pins to monitor these power supply voltages.
The ADM1026 has 8 pins that are general-purpose logic
I/O pins (pins 1,2 and 43 to 48), 1 pin that can be config-
ured as GPIO or as a thermal interrupt (THERM) output
(pin 42) and 8 pins that can be configured for fan speed
measurement or as general-purpose logic pins (pins 3 to 6
and 9 to 12).
SEQUENTIAL MEASUREMENT
When the ADM1026 monitoring sequence is started, it
cycles sequentially through the measurement of analog in-
puts and the temperature sensor, while at the same time
the fan speed inputs are independently monitored. Mea-
sured values from these inputs are stored in Value Regis-
ters. 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 17).
Any or all of the Interrupt Status Bits can be masked by
appropriate programming of the Interrupt Mask Registers.
CHASSIS INTRUSION
A chassis intrusion input (pin 16) is provided to detect
unauthorised tampering with the equipment. This event is
latched in a battery-backed up register bit.
RESETS
The ADM1026 has two power on reset outputs,
RESETMAIN and RESETSTBY, that are asserted when
3.3VMAIN or 3.3VSTBY fall below the reset threshold.
These give a 180ms reset pulse at power up. RESETMAIN
also functions as an active-low RESET input.
FAN SPEED CONTROL OUTPUTS
The ADM1026 has two outputs intended to control fan
speed, though they can also be used for other purposes.
Pin 22 is a pulse-width modulated (PWM) output with a
programmable duty-cycle and an output frequency of typi-
cally 75Hz.
Pin 23 is connected to the output of an on-chip, 8-bit
digital-to-analog converter with an output range of zero to
2.5V.
Either or both of these outputs may be 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 or remote temperature sensors.
INTERNAL REGISTERS OF THE ADM1026
The ADM1026 contains a large number of data registers.
A brief description of the principal registers is given be-
low. More detailed descriptions are given in the relevant
sections and in the tables at the end of the data sheet.
Address Pointer Register: This register contains the address
that selects one of the other internal registers. When writing to
the ADM1026, the first byte of data is always a register ad-
dress, which is written to the Address Pointer Register.
Configuration Registers: Provide control and configuration
for various operating parameters of the ADM1026.
Fan Divisor Registers: Contain counter pre-scaler values
for fan speed measurement.
Fan Speed Registers: Contain speed values for PWM and
DAC fan drive outputs.
GPIO Configuration Registers: These configure the
GPIO pins as input or output and for signal polarity.
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.
Status Registers: These registers store events from the
various interrupt sources.
Mask Registers: Allow masking of individual interrupt
sources.
EEPROM
The ADM1026 has 8kbytes of non-volatile, Electrically-
Erasable Programmable Read-Only Memory (EEPROM),
from register addresses 8000h to 9FFFh. This may be
used for permanent storage of data that will not be lost
when the ADM1026 is powered down, unlike the data in
