LM78 datasheet(21/31 Pages) NSC

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Functional Description (Continued)

8.0 THE LM78 INTERRUPT STRUCTURE

Figure 12 depicts the Interrupt Structure of the LM78. The

LM78 can generate Interrupts as a result of each of its

internal WATCHDOG registers on the analog, temperature,

and fan inputs. Overflow of the POST RAM (greater than 32

bytes written to POST RAM) will also cause an Interrupt.

External Interrupts can come from the following three

sources. While the labels suggest a specific type or source

of Interrupt, these labels are not restrictions of their usage,

and they 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.

output’s wire or’d to the BTI input of the LM78. If the

temperature 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 k

Ω.

DS012873-21

FIGURE 12. Interrupt Structure

LM78 Datasheet(PDF) 21 Page - National Semiconductor (TI)