Interfacing to μPs with

Bidirectional Reset Pins

μPs with bidirectional reset pins, such as the Motorola

68HC11 series, can contend with the MAX705–MAX708

RESET

output. If, for example, the RESET output is

driven high and the μP wants to pull it low, indeterminate

logic levels may result. To correct this, connect a 4.7kΩ

resistor between the RESET output and the μP reset I/O,

as in Figure 8. Buffer the RESET output to other system

components.

Figure 5. RESET Valid to Ground Circuit

Figure 7. Monitoring a Negative Voltage

Figure 6. Monitoring Both +5V and +12V

Figure 6. Monitoring Both +5V and +12V

MAX70_

RESET

R1

MAX70_

RESET

R2

R1

+5V

V-

PFI

GND

MR

PFO

TO µP

100kΩ

100kΩ

2N3904

MR

PFO

+5V

0V

+5V

0V

0V

V-

5 1.25

R1

1.25 VTRIP

R2

,VTRIP 0

–

=

–

<

MAX70_

RESET

130kΩ

1%

PARAMETER

MIN TYP MAX UNIT

+12V Reset

Threshold at +25°C

10.67 10.87 11.50

V

1MΩ

1%

+5V

+12V

PFI

GND

MR

PFO

TO µP

MAX70_

BUFFERED RESET TO OTHER SYSTEM COMPONENTS

4.7kΩ

GND

RESET

GND

RESET

µP

MAX705–MAX708/MAX813L

MAX705–MAX708/MAX813L

Low-Cost, μP Supervisory Circuits

www.maximintegrated.com

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