ADM1024
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23
Using the Configuration Registers
Control of the ADM1024 is provided through two
configuration registers. The ADC is stopped upon powerup,
and the INT_Clear signal is asserted, clearing the INT output.
The Configuration Registers are used to start and stop the
ADM1024; enable or disable interrupt outputs and modes,
and provide the initialization function described above.
Bit 0 of Configuration Register 1 controls the monitoring
loop of the ADM1024. Setting Bit 0 low stops the
monitoring loop and puts the ADM1024 into a low power
mode thereby reducing power consumption. Serial bus
communication is still possible with any register in the
ADM1024 while in low power mode. Setting Bit 0 high
starts the monitoring loop.
Bit 1 of Configuration Register 1 enables or disables the
INT Interrupt output. Setting Bit 1 high enables the INT
output; setting Bit 1 low disables the output.
Bit 2 of Configuration Register 1 enables or disables the
THERM output. Setting Bit 1 high enables the INT output;
setting Bit 1 low disables the output.
Bit 3 of Configuration Register 1 is used to clear the INT
interrupt output when set high. The ADM1024 monitoring
function will stop until Bit 3 is set low. Interrupt Status
register contents will not be affected.
Bit 4 of Configuration Register 1 causes a low going 45 ms
(typ) pulse at the RESET pin (Pin 12).
Bit 6 of Configuration Register 1 is used to clear an
interrupt at the THERM output when it is set to 1.
Bit 7 of Configuration Register 1 is used to start a
Configuration Register Initialization when it is set to 1.
Bit 0 of Configuration Register 2 is used to mask
temperature interrupts at the INT output when it is set to 1.
The THERM output is unaffected by this bit.
Bits 1 and 2 of Configuration Register 2 lock the values
stored in the Local and Remote Fan Control Registers at
addresses 13h and 14h. The values in these registers cannot
be changed until a power-on reset is performed.
Bit 3 of Configuration Register 2 selects the THERM
interrupt mode. The default value of 0 selects onetime
mode. Setting this bit to 1 selects ACPI mode.
Starting Conversion
The monitoring function (analog inputs, temperature, and
fan speeds) in the ADM1024 is started by writing to
Configuration Register 1 and setting Start (Bit 0) high. The
INT_Enable (Bit 1) should be set to 1, and INT Clear (Bit 3)
set to 0 to enable interrupts. The THERMenable bit (Bit 2)
should be set to 1 and the THERM Clear bit (Bit 6) should
be set to 0 to enable temperature interrupts at the THERM
pin. Apart from initially starting together, the analog
measurements and fan speed measurements proceed
independently, and are not synchronized in any way.
The time taken to complete the analog measurements
depends on how they are configured, as described
elsewhere. The time taken to complete the fan speed
measurements depends on the fan speed and the number of
tachometer output pulses per revolution.
Once the measurements have been completed, the results
can be read from the Value Registers at any time.
Reduced Power and Shutdown Mode
The ADM1024 can be placed in a low power mode by
setting Bit 0 of the Configuration Register to 0. This disables
the internal ADC. Full shutdown mode may then be
achieved by setting Bit 0 of the Test Register to 1. This turns
off the analog output and stops the monitoring cycle, if
running, but does not affect the condition of any of the
registers. The device will return to its previous state when
this bit is reset to 0.
Application Circuit
Figure
37 shows a generic application circuit using the
ADM1024. The analog monitoring inputs are connected to
the power supplies including two processor core voltage
inputs. The VID inputs are connected to the processor
voltage ID pins. There are two tachometer inputs from fans,
and the analog output is used to control the speed of a third
fan. An opto-sensor for chassis intrusion detection is
connected to the CI input. Of course, in an actual
application, every input and output may not be used, in
which case unused analog and digital inputs should be tied
to analog or digital ground as appropriate.