ASM811, ASM812
October 2003
rev 1.0
V
TH
5V
V
CC
VCC
VCC
100k
Ω
0V
ASM812
TRST
ASM811
Power Supply
Power Supply
RESET
MR
MR
RESET
5V
0V
MR
TMRST
100kΩ
GND
GND
5V
0V
ASM811
ASM812
RESET
RESET
5V
0V
Figures 2 & 3: RESET valid with VCC under 1.1V
Figure 1: Reset Timing and Manual Reset (MR)
Application Information
Reset Output Operation
In µP / µC systems it is important to have the processor and
the system begin operation from a known state. A reset
output to a processor is provided to prevent improper
operation during power supply sequencing or low voltage
brown-out conditions.
Negative VCC Transients
Typically short duration transients of 100mV amplitude and
20µs duration do not cause a false RESET. A 0.1µF capacitor
at VCC increses transient immunity.
Bidirectional Reset Pin Interfacing
The ASM811/812 are designed to monitor the system power
supply voltages and issue a reset signal when the levels are
out of range. RESET outputs are guaranteed to be active for
The ASM811/812 can interface with µP / µC bi-directional
reset pins by connecting a 4.7kΩ resistor in series with the
ASM811/812 reset output and the µP/µC bi-directional reset
VCC above 1.1V. When VCC exceeds the reset threshold, an
input pin.
BUF
Buffered
RESET
internal timer keeps RESET active for the reset timeout
period, after which RESET becomes inactive (HIGH for the
ASM811 and LOW for the ASM812). If VCC drops below the
VCC
reset threshold, RESET automatically becomes active.
Alternatively, external circuitry or an operator can initiate this
condition using the Manual Reset (MR) pin. MR can be left
open if it is not used. MR can be driven by TTL/CMOS logic
or even an external switch.
µC or µP
ASM811
Power supply
4.7kΩ
RESET
Input
MR
RESET
GND
GND
Valid Reset with VCC under 1.1V
To ensure logic inputs connected to the ASM811 RESET pin
Bi-directional I/O Pin
are in a known state when VCC is under 1.1V, a 100kΩ pull-
Figure 4: Bi-directional Reset Pin Interface
down resistor at RESET is needed. The value is not critical.
A 100kΩ pull-up resistor to VCC is needed with the ASM812.
3 of 10
4 Pin µP Voltage Supervisor with Manual Reset
Notice: The information in this document is subject to change without notice
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
