Functional Description (Continued)
8.0 THE LM80 INTERRUPT STRUCTURE
DS100040-18
FIGURE 10. Interrupt Structure
Figure 10 depicts the Interrupt Structure of the LM80. The
LM80 can generate Interrupts as a result of each of its inter-
nal WATCHDOG registers on the analog, temperature, and
fan inputs.
•
CI (Chassis Intrusion) - This is an active high interrupt
from any type of device that detects and captures chassis
intrusion violations. This could be accomplished me-
chanically, optically, or electrically, and circuitry external
to the LM80 is expected to latch the event. The design of
the LM80 allows this input to go high even with no power
applied to the LM80, and no clamping or other interfer-
ence with the line will occur. This line can also be pulled
low for at least 10 ms by the LM80 to reset a typical
Chassis Intrusion circuit. Accomplish this reset by setting
Bit 5 of Configuration Register high. The bit in the Regis-
ter is self-clearing.
8.1 INTERRUPT INPUTS
External Interrupts can come from the following sources.
While the label suggests a specific type or source of Inter-
rupt, this label is not a restriction of its usage, and it could
come from any desired source:
•
BTI - This is an active low Interrupt intended to come
from the O.S. output of LM75 temperature sensors. The
LM75 O.S. output goes active when its temperature ex-
ceeds a programmed threshold. Up to 8 LM75’s can be
connected to a single Serial Bus bus with their O.S. out-
put’s wire or’d to the BTI input of the LM80. If the tem-
perature of any LM75 exceeds its programmed limit, it
drives BTI low. This generates an Interrupt to notify the
host of a possible overtemperature condition. Provides
an internal pull-up of 10 kΩ.
19
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