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1/8December 2003
AN1790
APPLICATION NOTE
How to Connect ST Reset Circuits to a Microprocessor
CONTENTS
■ INTRODUCTION
■ RESET THRESHOLDS
■ RESET OUTPUT
■ MANUAL RESET INPUT
■ CONNECTING THE
RESET CIRCUITS IN AN
APPLICATION
– Connection in a Noisy
Environment
– Connection to a Bi-direc-
tional Microprocessor
Reset
– Connection With Reset
Output Valid Down to
VCC = 0V
■ CONCLUSION
■ REFERENCES
■ REVISION HISTORY
This Application Note describes how to connect the STM809,
STM810, STM811 and STM812 Reset Circuits to Microproces-
sor Systems.
Further information on Reset Circuits can be found in the
STM809, STM810, STM811, STM812 datasheet on
www.st.com.
INTRODUCTION
All digital systems require the power supply to be controlled
during power-up and normal operations. Noise resulting from
ground loops or switching many signals at once, can create
glitches in the power supply which can cause the system to
malfunction.
For this reason ST has developed a new type of low-power su-
pervisory device, called Reset Circuits, specifically to monitor
power supplies. The Reset Circuits, STM809, STM810,
STM811, STM812, assert a reset signal whenever the power
supply drops below a preset threshold value, and keep it as-
serted until the voltage rises above that threshold for a mini-
mum period of time. The STM811 and STM812 also provide a
push-button reset input signal (MR
).
