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