Operation

STM6717/6718/6719/6720/STM6777/6778/6779/6780

10/30

Doc ID 11469 Rev 7

2

Operation

2.1

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 4.7 k

Ω resistor between RST and the processor’s reset I/O as

shown in Figure 11.

2.

The STM67xx supervisors are guaranteed to be in the correct RST output logic state

Figure 12) 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

adequate.

Figure 11.

STM67xx interface to processor with bi-directional reset pins

Figure 12.

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