LM80

SNIS102F – JUNE 1999 – REVISED MARCH 2013

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Configuration Register INITIALIZATION is accomplished by setting Bit 7 of the Configuration Register high. This

Bit automatically clears after being set.

The LM80 can be reset to it's “power on state” by taking NTEST_IN/Reset_IN pin low for at least 50 ns.

Using the Configuration Register

The Configuration Register provides all control over the LM80. At power on, the ADC is stopped and INT_Clear

is asserted, clearing the INT and RST_OUT/OS hardwire outputs. The Configuration Register starts and stops

the LM80, enables and disables INT outputs, clears and sets CI and GPO I/O pins, initiates reset pulse on

RST_OUT/OS pin, and provides the Reset function described in Resets.

Bit 0 of the Configuration Register controls the monitoring loop of the LM80. Setting Bit 0 low stops the LM80

monitoring loop and puts the LM80 in shutdown mode, reducing power consumption. Serial Bus communication

is possible with any register in the LM80 although activity on these lines will increase shutdown current, up to as

much as maximum rated supply current, while the activity takes place. Taking Bit 0 high starts the monitoring

loop, described in more detail subsequently.

Bit 1 of the Configuration Register enables the INT Interrupt hardwire output when this bit is taken high.

Bit 2 of the Configuration Register defines whether the INT pin is open source or open drain.

Bit 3 clears the INT output when taken high. The LM80 monitoring function will stop until bit 3 is taken low. The

content of the Interrupt (INT) Status Registers will not be affected.

Bit4, when taken high, will initiate a 10 ms RESET signal on the RST_OUT/OS output (when this pin is in the

RST mode).

When bit 5 is taken high the CI (Chassis Intrusion) pin is reset.

Bit 6 of the configuration register sets or clears the GPO output. This pin can be used in software power control

by activating an external power control MOSFET.

Starting Conversions

3.4 STARTING CONVERSION The monitoring function (Analog inputs, temperature, and fan speeds) in the

LM80 is started by writing to the Configuration Register and setting INT_Clear (Bit 3), low, and Start (Bit 0), high.

The LM80 then performs a round-robin monitoring of all analog inputs, temperature, and fan speed inputs

approximately once a second. If the temperature resolution is set to 12 bits one complete monitoring function will

take approximately 2 seconds. The sequence of items being monitored corresponds to locations in the Value

RAM (except for the Temperature reading) and is:

1. Temperature

2. IN0

3. IN1

4. IN2

5. IN3

6. IN4

7. IN5

8. IN6

9. Fan 1

10. Fan 2

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 the conversion is

read, reads of any single value should not be done more often than once every 120 ms. When reading all values

with the temperature resolution set to 9-bits, allow at least 1.5 seconds between reading groups of values.

Reading more frequently than once every 1.5 seconds can also prevent complete updates of Interrupt Status

Registers and Interrupt Outputs. If the temperature resolution is set to 12-bit, allow at least 2.0 seconds between

reading groups of values.

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