V

CC

RESET

GND

LM809

V

CC

RESET

GND

BUFFER

4.7 k

Buffered

to other system

components

RESET

µP

9

LM809, LM810

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SNVS052E – SEPTEMBER 1999 – REVISED APRIL 2016

Product Folder Links: LM809 LM810

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Copyright © 1999–2016, Texas Instruments Incorporated

7.3.1.3 Interfacing to µPs with Bidirectional Reset Pins

Microprocessors with bidirectional reset pins, such as the Motorola 68HC11 series, can be connected to the

LM809 RESET output. To ensure a correct output on the LM809 even when the microprocessor reset pin is in

the opposite state, connect a 4.7-k

Ω resistor between the LM809 RESET output and the µP reset pin, as shown

in Figure 9. Buffer the LM809 RESET output to other system components.

Figure 9. Interfacing to Microprocessors with Bidirectional Reset I/O

7.4 Device Functional Modes

7.4.1 VCC Supply Voltage Low

When VCC supply voltage declines below the reset threshold, the RESET output is asserted. For LM809, the

active-low RESET output is low. For LM810, the active-high RESET output is high.

7.4.2 VCC Supply Voltage High

When the VCC supply voltage rises above the reset threshold, the RESET output resets after 240 ms. For LM809,

the active-low RESET output rises high. For LM810, the active-high RESET output drops low.