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Notice: The information in this document is subject to change without notice

µP Supervisory Circuit

ASM161 / ASM162

rev 1.0

October 2003

Detailed Descriptions

The reset function ensures the microprocessor is properly

reset and powers up into a known condition after a power

failure.

Reset Timing

A reset is generated whenever the supply voltage is below

guaranteed to be no more than 2 seconds. The rest signal

remains active as long as the monitored supply voltage is

below the internal threshold voltage.

The ASM161 has an open-drain, active LOW RESET output

to 1.1 V). The ASM161 uses an external pull-up resistor.

Output leakage current is under 1µA. A high resistance value

can be used to minimize current drain.

The ASM162 generates an active-HIGH RESET output.

Manual Reset

The ASM161/162 have a unique manual reset circuit. A

negative going edge transition on MR initiates the reset. A

manual reset generates a single reset pulse of fixed length.

The output-reset pulse remains asserted for the Reset Active

completed, the MR input remains disabled for at least 49µS

During the MR disabled period, the microcontroller is

guaranteed a time period free of new manual reset signals.

This period can be used to refresh critical DRAM contents or

other system tasks.

The MR pin must be taken HIGH and LOW again after the

pulse.

The manual reset input has an internal 20k

Ω pull-up resistor.

MR can be left open if not used.

Application Information

Glitch Resistance

The ASM161/162 are relatively immune to short duration

goes 100mV below the reset threshold and lasts 20s or less

will not typically cause a reset pulse.

To ensure that logic inputs connected to the ASM162 RESET

pull-down resistor at RESET is needed. The value is not

critical.

This scheme does not work with the open-drain outputs of

ASM161.

Part Number

Reset Polarity

ASM161

LOW (use external pull-up resistor)

ASM162

HIGH

MR input is blocked

Ready

Reset

*Second and following edges ignored

*........

next

Triggering

Figure 1: Manual Reset Timing

Time-Out

Pulse

for

MR

RESET

MR

Power Supply

ASM162

RESET

GND

MR

Figure 2: RESET valid with VCC under 1.1V

100KΩ