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http://www.union-ic.com Rev.01 Jan.2015

11/17

UM807/821/822

Figure 4. RESET

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Interfacing to μPs with Bidirectional Reset Pins

μPs with bidirectional reset pins (such as the Motorola68HC11 series) can contend with the

UM821/822 reset outputs. If, for example, the UM821 RESET

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output is asserted high and the μP

wants to pull it low, indeterminate logic levels may result. To correct such cases, connect a 4.7kΩ

resistor between the UM821 RESET

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(or UM822 RESET) output and the μP reset I/O (Figure 5).

Buffer the reset output to other system components.

BUFFER

UM821

RESET

GND

4.7k

µP

RESET

GND

Buffered RESET

to Other System

Components

Figure 5. Interfacing to μPs with Bidirectional Reset I/O

UM821