Monitoring an Additional Power Supply

These µP supervisors can monitor either positive or

negative supplies using a resistor voltage divider to

PFI. PFO can be used to generate an interrupt to the µP

or to cause reset to assert (Figure 12).

Interfacing to µPs with

Bidirectional Reset Pins

Since the RESET output is open drain, the MAX793/

MAX794/MAX795 interface easily with µPs that have

bidirectional reset pins, such as the Motorola 68HC11.

Connecting the RESET output of the µP supervisor

directly to the RESET input of the microcontroller with a

single pullup resistor allows either device to assert

reset (Figure 17).

These supervisors are relatively immune to short-dura-

ing resets to the µP during power-up, power-down, and

brownout conditions. Therefore, resetting the µP when

ommended.

3.0V/3.3V Adjustable Microprocessor

Supervisory Circuits

______________________________________________________________________________________

17

MAX793

MAX794

GND

0V

TO

µP

PFI

PFO

R1

R2

R3

*OPTIONAL

C1*

PFO

0V

R1 + R2

R2

+

R1

1

+

R2

1

R3

1

–

R3

WHERE

GND

TO

µP

PFI

PFO

R1

R2

R3

*OPTIONAL

C1*

R1 + R2

)

R2

(

+

R1

1

+

R2

1

R3

1

–

R3

WHERE

MAX793

MAX794

0V

PFO

0V

(b)

(a)

(

)

(

)

(

)

+

R1

1

+

R2

1

R3

1

(

)

MAX793

MAX794

MAX795

GND

N

RESET

GENERATOR

GND

RESET

RESET

µP

Figure 17. Interfacing to µPs with Bidirectional Reset I/O