ASM161JCUSSLASHT datasheet(3/9 Pages) PULSECORE

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April 2008

ASM161/ASM162

rev 1.5

µP Supervisory Circuit

3 of 9

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

Pin Description

Pin #

ASM161

ASM162

Name

Function

GND

Ground.

RESET

Active-LOW, open-drain reset output. RESET remains LOW while VCC is

below the reset threshold and for 800ms minimum after VCC rises above the

reset threshold. An external pull-up resistor is needed.

RESET

Active HIGH reset output. RESET remains HIGH while VCC is below the

reset threshold and for 800ms after VCC rises above the reset threshold.

Manual reset input. A negative going edge transition on MR asserts reset.

Reset remains asserted for one reset time-out period (800 ms min). This

active-LOW input has an internal pull-up resistor. It can be driven from a

TTL or CMOS logic line or shorted to ground with a switch. Leave open if

unused.

VCC

Power supply input voltage.

Detailed Description

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 the threshold level (VCC < VTH). The reset duration

is at least 800ms after VCC has risen above the reset

threshold and is 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 (which is guaranteed to be in the correct state for

VCC down 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.

Part Number

Reset Polarity

ASM161

LOW (use external pull-up resistor)

ASM162

HIGH

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 Time-Out Period tRP and then clears. Once

the reset pulse is completed, the MR input remains

disabled for at least 49µS but not more than 122µS. This

period is specified as tMRD.

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 tMRD period has been completed to initiate another

reset pulse.

The manual reset input has an internal 20k

Ω pull-up

resistor. MR can be left open if not used.

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