STM6717/6718/6719/6720/6777/6778/6779*/6780*

8/25

OPERATION

Applications Information

1.

Interfacing to Processors with Bi-directional

Reset Pins

Most processors with bi-directional reset pins

can interface directly to the open drain RST

outputs (STM6717/19/77/79). Systems

simultaneously requiring a push-pull RST

output and a bi-directional reset interface can

be in logic contention. To prevent this

contention, connect a 4.7k

Ω resistor between

RST and the processor’s Reset I/O as shown

in Figure 12.

2.

Ensuring a Valid RST Output Down to

The STM67xx Supervisors are guaranteed to

be in the correct RST output logic state when

applications which require valid reset levels

active-low outputs (push-pull only, see Figure

13.) will ensure that the reset line is valid while

the reset output can no longer sink or source

current. This scheme does NOT work with the

open drain outputs of the STM6717/19/77/79.

The resistor value used is not critical, but it

must be large enough not to load the reset

For most applications, 100k

Ω is adequate.

Figure 12. STM67xx Interface to Processor with Bi-directional Reset Pins

AI10425

VCC1

VCC2

VSS

VCC1

STM67xx

RST

To other

system

components

4.7k

Ω

VCC2

VSS

Processor

RESET

AI10426

VCC1

VCC1

VSS

STM67xx

RST

R1