參數(shù)資料
型號(hào)： LM81CIMTX-32
廠商： National Semiconductor Corporation
英文描述： Serial Interface ACPI-Compatible Microprocessor System
中文描述： 串行接口ACPI的兼容微處理器系統(tǒng)
文件頁數(shù)： 9/32頁
文件大小： 412K
代理商： LM81CIMTX-32
Test Circuit
Functional Description
1.0 GENERAL DESCRIPTION
The LM81 provides 6 analog inputs, a temperature sensor, a
Delta-Sigma ADC (Analog-to-Digital Converter), a DAC out-
put, 2 fan speed counters, WATCHDOG registers, and a va-
riety of inputs and outputs on a single chip. A two wire Serial
Bus interface is included. The LM81 performs power supply,
temperature, fan control and fan monitoring for personal
computers.
The analog inputs are useful for monitoring several power
supplies present in a typical computer. The LM81 includes
internal resistor dividers that scale and/or offset external
Vccp, +2.5V, +3.3V, +5.0V and +12V power supply voltages
to a 3/4 scale nominalADC output. The LM81ADC then con-
tinuously converts the scaled inputs to 8-bit digital words.
Measurement of negative voltages (such as -5V and -12V
power supplies) can be accommodated with an external re-
sistor divider applied to the Vccp2 input. Temperature is con-
verted to a 9-bit or 12-bit two’s-complement digital word with
a 0.5C LSB or 0.0625C LSB, respectively.
Fan inputs measure the period of tachometer pulses from
the fans, providing a higher count for lower fan speeds. The
fan inputs are Schmitt-Trigger digital inputs with an accept-
able range of 0V to V
+
and a transition level of approximately
V
+
/2. Full scale fan counts are 255 (8-bit counter) and this
represents a stopped or very slow fan. Nominal speeds,
based on a count of 153, are programmable from 1100 to
8800 RPM on FAN1 and FAN2. Schmitt-Trigger input cir-
cuitry is included to accommodate slow rise and fall times. A
0V to 1.25V DAC output voltage range can be used for con-
trol of fan speed.
The LM81 has several internal registers, as shown in Figure
4 Table 1 and Section 13.0 These include:
Configuration Register:
figuration.
Interrupt Status Registers:
status of each WATCHDOG limit or Interrupt event.
Interrupt Mask Registers:
vidual Interrupt sources, as well as separate masking for
each of the two hardware Interrupt outputs.
Provides control and con-
Two registers to provide
Allows masking of indi-
CI Clear Register:
pulse on the chassis intrusion pin (CI).
VID/Fan Divisor Register:
state of the VID0-VID3 input lines and the divisor bits for
FAN1 and FAN2 inputs.
Serial Bus Address Register:
address. At power on it assumes the default value of
01011XX binary, and can be altered by the state of A0
and A1.
VID4 Register:
Contains the state of the VID4 input.
Temperature Configuration Register:
terrupt mode and contains the 0.5C LSB of the tempera-
ture reading.
Extended Mode Registers:
Extended Mode which includes the LSBs of the 12-bit
temperature reading, T_CRIT, and T
HYST
Value RAM:
The DAC digital input, 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 34 bytes, ad-
dresses 15h - 3Fh, containing:
— byte 1 at address 15h a manufacturers test register
— locations 16h - 18h are unassigned and do not have
associated registers
— byte 2 at address 19h contains the DAC Data Register
— locations 1Ah - 1Fh are unassigned and do not have
associated registers
— the next 10 bytes at addresses 20h -29h contain all of
the results, with address 26h reserved
— the next 18 bytes at addresses 2Bh-3Ch are the
WATCHDOG limits
— the last 2 bytes at addresses 3Eh and 3Fh contain the
Company ID and Stepping ID numbers, respectively
When the LM81 is started, it cycles through each measure-
ment in sequence, and it continuously loops through the se-
quence approximately once every 400 ms. Each measured
value is compared to values stored in WATCHDOG, or Limit
registers. When the measured value violates the pro-
grammed limit the LM81 will set a corresponding Interrupt in
the Interrupt Status Registers. The hardware Interrupt line
INT is fully programmable with separate masking of each In-
Allows transmitting a 20 ms low
This register contains the
Contains the Serial Bus
Selects the in-
Enable and control the
DS100072-6
FIGURE 3. Digital Output Load Test Circuitry
www.national.com
9
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