LM81Serial Interface ACPI-Compatible Microprocessor SystemHardware MonitorGeneral DescriptionThe LM81 is a highly integrated data acquisition system f
Test CircuitFunctional Description1.0 GENERAL DESCRIPTIONThe LM81 provides 6 analog inputs, a temperature sensor, aDelta-Sigma ADC (Analog-to-Digital
Functional Description (Continued)Interrupt source. In addition, the Configuration Register hasa control bit to enable or disable the hardware Interru
Functional Description (Continued)2.1 Internal Registers of the LM81TABLE 1. The internal registers and their corresponding internal LM81 addresses ar
Functional Description (Continued)2.2 Serial Bus InterfaceThe Serial Bus control lines consist of the SMBData (serialdata), SMBCLK (serial clock) and
Functional Description (Continued)3.0 USING THE LM813.1 Power OnWhen power is first applied, the LM81 performs a “power onreset” on several of its reg
Functional Description (Continued)3.5 Reading Conversion ResultsThe conversion results are available in the Value RAM.Conversions can be read at any t
Functional Description (Continued)equal to its LOW limit will cause a flag to be set in itsInterrupt Status Register. This flag will activate the INT
Functional Description (Continued)Counts are based on 2 pulses per revolution tachometer outputs.RPM Time per Revolution Counts for “Divide by 2” Comm
Functional Description (Continued)7.0 DAC OUTPUTThe LM81 provides an 8-bit DAC (Digital-to-Analog Con-verter) with an output range of 0 to 1.25 volts
Functional Description (Continued)8.0 TEMPERATURE MEASUREMENT SYSTEMThe LM81 temperature sensor and ADC produce 9-bit or12-bit two’s-complement temper
Ordering InformationTemperature RangeNS PackageNumber−40˚C ≤ TA≤ +125˚C SMBusRevisionLevelVoltageMonitoringErrorOrder Number Device MarkingLM81BIMT-31
Functional Description (Continued)8.2 Temperature InterruptsINT and T_CRIT_A outputs are provided for temperatureinterrupt. Temperature interrupts hav
Functional Description (Continued)Extended Repetitive Interrupt Mode is shown inFigure 14and operates in the following way: Once activated, all inter-
Functional Description (Continued)9.0 THE LM81 INTERRUPT STRUCTUREFigure 17depicts the Interrupt Structure of the LM81. TheLM81 can generate Interrupt
Functional Description (Continued)masks for each Interrupt. As described in Section 3.3, thehardware Interrupt line can also be enabled/disabled in th
Functional Description (Continued)12.0 FAN MANUFACTURERSManufacturers of cooling fans with tachometer outputs arelisted below:NMB Tech9730 Independenc
Functional Description (Continued)13.0 REGISTERS AND RAM13.1 Address RegisterThe main register is the ADDRESS Register. The bit designations are as fo
Functional Description (Continued)13.3 Configuration Register—Address 40hPower on default –<7:0>= 00001000 binaryBit Name Read/WriteDescription0
Functional Description (Continued)13.4 Interrupt Status Register 1—Address 41hPower on default –<7:0>= 0000 0000 binaryBit Name Read/Write Descr
Functional Description (Continued)13.7 Interrupt Mask Register 2—Address 44hPower on default –<7:0>= 0000 0000 binaryBit Name Read/WriteDescript
Functional Description (Continued)13.10 VID/Fan Divisor Register—Address 47hPower on default –<7:4>is 0101, and<3:0>is mapped to VID<3:
Block DiagramPin DescriptionPinName(s)PinNumberNumberof PinsType DescriptionA0/NTEST_OUT 1 1 Digital I/0 The lowest order programmable bit of the seri
Functional Description (Continued)13.14 Extended Mode Register 1—Address 4ChPower on default –<7:0>= 0100 0100 binaryBit Name Read/Write Descrip
Functional Description (Continued)13.16 Value RAM—Address 15h–3FhAddress A6–A0 Description15h Manufacturers Test Register19h DAC data register; power
Typical ApplicationDS100072-23FIGURE 19. In this PC application the LM81 monitors temperature, fan speed for 2 fans, and 6 powersupply voltages. It al
Physical Dimensions inches (millimeters) unless otherwise notedLIFE SUPPORT POLICYNATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENT
Pin Description (Continued)PinName(s)PinNumberNumberof PinsType DescriptionINT10 1 Digital Output Interrupt active low open-drain output. This output
Absolute Maximum Ratings (Notes 1, 2)If Military/Aerospace specified devices are required,please contact the National Semiconductor Sales Office/Distr
DC Electrical Characteristics (Continued)The following specifications apply for +2.8VDC≤ V+≤ +3.8VDC,RS= 500Ω, unless otherwise specified. Boldface li
DC Electrical Characteristics (Continued)The following specifications apply for +2.8VDC≤ V+≤ +3.8VDC,RS= 500Ω, unless otherwise specified. Boldface li
AC Electrical CharacteristicsThe following specifications apply for +2.8VDC≤ V+≤ +3.8VDCon SMBCLK and SMBData, unless otherwise specified. Bold-face l
AC Electrical Characteristics (Continued)Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratin
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