LM87 datasheet(16/45 Pages) TI2

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LM87

SNAS034J – APRIL 2000 – REVISED MARCH 2013

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Starting Conversions

The monitoring function (Analog inputs, temperature, and fan speeds) in the LM87 is started by writing to

Configuration Register 1 and setting INT_Clear (Bit 3) low, and Start (bit 0) high. The LM87 then performs a

“round-robin” monitoring of all analog inputs, temperature, and fan speed inputs approximately once every 0.3 s.

The sequence of items being monitored is:

1. Check D1 connections

2. Check D2 connections

3. Internal Temperature

4. External D1 Temperature

5. External D2 Temperature

6. +2.5V

7. +Vccp1

8. Vcc 3.3V

9. Vcc 5.0V

10. +5Vin

11. +12Vin

12. +Vccp2

13. AIN1

14. AIN2

15. Fan 1

16. Fan 2

DACOut immediately changes after the DAC Data Register in the Value RAM has been updated. For a zero to

full scale transition DACOut will typically settle within 100

μsec of the stop by master in the write to the DAC Data

Configuration Register.

Reading Conversion Results

The conversion results are available in the Value RAM. Conversions can be read at any time and will provide the

result of the last conversion. Because the ADC stops, and starts a new conversion whenever it is read, reads of

any single value should not be done more often than once every 56 ms. When reading all values, allow at least

0.6 seconds between reading groups of values. Reading more frequently than once every 0.6 seconds can also

prevent complete updates of Interrupt Status Registers and Interrupt Output's.

A typical sequence of events upon power on of the LM87 would consist of:

1. Set WATCHDOG Limits

2. Set Interrupt Masks

3. Start the LM87 monitoring process

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