LM87CIMT/NOPB National Semiconductor, LM87CIMT/NOPB Datasheet - Page 9

• Manufacturer Part Number: LM87CIMT/NOPB
• Description: IC INTERFACE SER MONITOR 24TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM87CIMT/NOPB

• Function: Hardware Monitor
• Topology: ADC (Sigma Delta), Comparator, Fan Speed Control, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: I²C™/SMBus™
• Output Alarm: No
• Output Fan: Yes
• Voltage - Supply: 2.8 V ~ 3.8 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 24-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM87CIMT; *LM87CIMT/NOPB; LM87CIMT

to accommodate slow rise and fall times. An 8 bit DAC with
0 V to 2.5 V output voltage range can be used for control of
fan speed.
The LM87 has several internal registers, as shown in
4,
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Table 1
Configuration Registers:
configuration.
Channel Mode Register:
the dual purpose input pins, scaling for internal Vcc
measurement, and operation of some IRQ inputs.
Interrupt Status Registers:
status of each WATCHDOG limit or Interrupt event.
Reading the Status Registers clears any active bits.
Interrupt Status Mirror Registers:
provide status of each WATCHDOG limit or Interrupt
event. Reading the Mirror Registers does not affect the
status bits.
Interrupt Mask Registers:
Interrupt sources, as well as separate masking for each of
the two hardware Interrupt outputs.
CI Clear Register:
(minimum) low pulse on the chassis intrusion pin (CI).
VID/Fan Divisor Register: This register contains the
state of the VID0-VID3 input lines and the divisor bits for
FAN1 and FAN2 inputs.
VID4 Register: Contains the state of the VID4 input.
Extended Mode Register:
Response operation.
Hardware High Limit Registers:
14h, 17h and 18h where Internal and External 'Hardware'
WATCHDOG temperature high limits are stored. These
limits have Power On Default settings but can be adjusted
by the user. The values stored at 13h and 14h can be
locked down by setting bits 1 and 2 of Configuration
Register 2.
and Section 13.0. These include:
Allows transmitting a 20 ms
Controls the functionality of
Allows masking of individual
Enable and control the Alert
Provide control and
Two registers to provide
Registers at 13h,
Two registers to
Figure
9
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When the LM87 is started, it cycles through each measure-
ment in sequence, and it continuously loops through the
sequence approximately once every 0.4 s. Each measured
value is compared to values stored in WATCHDOG, or Hard-
ware High Limit registers. When the measured value violates
the programmed limit the LM87 will set a corresponding In-
terrupt in the Interrupt Status Registers. The hardware Inter-
rupt line INT# is fully programmable with separate masking of
each Interrupt source. In addition, the Configuration Register
has a control bit to enable or disable the hardware Interrupt.
Another hardware Interrupt line available, THERM# is used
to signal temperature specific events. Having a dedicated in-
terrupt for these conditions allows specific actions to be taken
for thermal events. This output is enabled by setting bit 2 of
Configuration Register 1.
The Chassis Intrusion input is designed to accept an active
high signal from an external circuit that activates and latches
when the case is removed from the computer.
Value and Limit RAM:
monitoring results (temperature, voltages, fan counts),
WATCHDOG limits, and Company/Stepping IDs are all
contained in the Value RAM. The Value RAM consists of
a total of 33 bytes, addresses 19h - 3Fh, containing:
— byte 1 at address 19h contains the DAC Data Register
— locations 1Ah and 1Bh contain the WATCHDOG low
limits for AIN1 and AIN2
— locations 1Ch - 1Fh are unassigned and do not have
associated registers
— the next 10 bytes at addresses 20h -29h contain all of
the results
— location 2Ah is unassigned and does not have an
associated register
— the next 18 bytes at addresses 2Bh-3Ch are the
remaining WATCHDOG limits
— the last 2 bytes at addresses 3Eh and 3Fh contain the
Company ID and Stepping ID numbers, respectively
The DAC digital output,
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