Analog Devices dBCool ADT7476, Руководство пользователя

Страница: 25 / 72

ADT7476
Rev. B | Page 25 of 72
LIMITS, STATUS REGISTERS, AND INTERRUPTS
LIMIT VALUES
Associated with each measurement channel on the ADT7476
are high and low limits. These can form the basis of system
status monitoring. A status bit can be set for any out-of-limit
condition and is detected by polling the device. Alternatively,
SMBALERT
interrupts can be generated to flag out-of-limit
conditions to a processor or microcontroller.
8-Bit Limits
The following is a list of 8-bit limits on the ADT7476.
Voltage Limit Registers
Register 0x44, 2.5 V Low Limit = 0x00 default
Register 0x45, 2.5 V High Limit = 0xFF default
Register 0x46, V
CCP
Low Limit = 0x00 default
Register 0x47, V
CCP
High Limit = 0xFF default
Register 0x48, V
CC
Low Limit = 0x00 default
Register 0x49, V
CC
High Limit = 0xFF default
Register 0x4A, 5 V Low Limit = 0x00 default
Register 0x4B, 5 V High Limit = 0xFF default
Register 0x4C, 12 V Low Limit = 0x00 default
Register 0x4D, 12 V High Limit = 0xFF default
Temperature Limit Registers
Register 0x4E, Remote 1 Temperature Low Limit = 0x81 default
Register 0x4F, Remote 1 Temperature High Limit = 0x7F default
Register 0x6A, Remote 1 THERM Temperature Limit = 0x64
default
Register 0x50, Local Temperature Low Limit = 0x81 default
Register 0x51, Local Temperature High Limit = 0x7F default
Register 0x6B, Local THERM Temperature Limit = 0x64 default
Register 0x52, Remote 2 Temperature Low Limit = 0x81 default
Register 0x53, Remote 2 Temperature High Limit = 0x7F default
Register 0x6C, Remote 2 THERM Temperature Limit = 0x64
default
THERM Limit Register
Register 0x7A, THERM Timer Limit = 0x00 default
16-Bit Limits
The fan TACH measurements are 16-bit results. The fan TACH
limits are also 16 bits, consisting of a high byte and low byte.
Because fans running under speed or stalled are normally the
only conditions of interest, only high limits exist for fan TACHs.
Because the fan TACH period is actually being measured,
exceeding the limit indicates a slow or stalled fan.
Fan Limit Registers
Register 0x54, TACH1 Minimum Low Byte = 0xFF default
Register 0x55, TACH1 Minimum High Byte = 0xFF default
Register 0x56, TACH2 Minimum Low Byte = 0xFF default
Register 0x57, TACH2 Minimum High Byte = 0xFF default
Register 0x58, TACH3 Minimum Low Byte = 0xFF default
Register 0x59, TACH3 Minimum High Byte = 0xFF default
Register 0x5A, TACH4 Minimum Low Byte = 0xFF default
Register 0x5B, TACH4 Minimum High Byte = 0xFF default
Out-of-Limit Comparisons
Once all limits have been programmed, the ADT7476 can be
enabled for monitoring. The ADT7476 measures all voltage and
temperature measurements in round-robin format and sets the
appropriate status bit for out-of-limit conditions. TACH meas-
urements are not part of this round-robin cycle. Comparisons
are done differently depending on whether the measured value
is being compared to a high or low limit.
High Limit > Comparison Performed
Low Limit
≤
Comparison Performed
Voltage and temperature channels use a window comparator for
error detecting and, therefore, have high and low limits. Fan
speed measurements use only a low limit. This fan limit is
needed only in manual fan control mode.
Analog Monitoring Cycle Time
The analog monitoring cycle begins when a 1 is written to the
start bit (Bit 0) of Configuration Register 1 (0x40). The ADC
measures each analog input in turn, and, as each measurement
is completed, the result is automatically stored in the appro-
priate value register. This round-robin monitoring cycle
continues unless disabled by writing a 0 to Bit 0 of Configur-
ation Register 1.
Because the ADC is normally left to free-run in this manner,
the time taken to monitor all the analog inputs is normally not
of interest; the most recently measured value of any input can
be read out at any time.
www.BDTIC.com/ADI