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 4.7k

Ω

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

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

components.

Low-Cost, µP Supervisory Circuits

8

_______________________________________________________________________________________

MAX70_

RESET

R2

R1

+5V

V-

PFI

GND

MR

PFO

TO

µP

100k

100k

2N3904

MR

PFO

+5V

0V

+5V

0V

0V

V-

Figure 7. Monitoring a Negative Voltage

MAX70_

BUFFERED RESET TO OTHER SYSTEM COMPONENTS

4.7k

GND

RESET

GND

RESET

µP

Figure 8. Interfacing to µPs with Bidirectional Reset I/O

5

1.25

R1

1.25

VTRIP

R2

,VTRIP

0

−

=

−

<

MAX70_

RESET

R1

Figure 5. RESET Valid to Ground Circuit

MAX70_

RESET

130k

1%

PARAMETER

MIN

TYP

MAX

UNIT

+12V Reset

Threshold at +25°C

10.67 10.87 11.50

V

1M

1%

+5V

+12V

PFI

GND

MR

PFO

TO

µP

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