Datasheet
LM87
SNAS034J –APRIL 2000–REVISED MARCH 2013
www.ti.com
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
Register Serial Bus transaction. The DAC Data Register is not reset by the INITIALIZATION bit found in the
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
16 Submit Documentation Feedback Copyright © 2000–2013, Texas Instruments Incorporated
Product Folder Links: LM87