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ILC1232

mP Supervisory Circuit

Impala Linear Corporation 

ILC1232 mP Supervisory Circuit

Sept 1999

Circuit Decription

Power Monitor

The RST and RST pins are asserted whenever VCC falls

below the reset threshold voltage set by the TOL pin. A 5%

tolerance level (4.62V reset threshold voltage) can be

selected by connecting the TOL pin to ground or a 10% tol-

erance (4.37V reset threshold voltage) can be selected by

connecting the TOL pin to VCC. The reset pins will remain

asserted for a period of 250ms after VCC has risen above

the reset threshold voltage. The reset function ensures the

microprocessor is properly reset and powers up into a

known condition after a power failure. RST will remain valid

with VCC as low as 1.4V.

VCC

VCCTP

VCCTP

Pushbutton Reset Input

The PBRST input can be driven with a manual pushbutton

switch or with external logic signals. The input is internally

debounced and requires an active low signal to force the

reset outputs into their active states. The PBRST input will

recognize any pulse that is 20ms in duration or greater and

will ignore all pulses that are less than 1ms in duration.

PBRST

tPB

tPDLY

RST

tRST

tRPD

RST

tRPU

RST

Pushbutton Reset

RST

Power-Up/Power-Down Sequence

Watchdog Timer

The microprocessor can be monitored by connecting the ST

pin (watchdog input) to a bus line or I/O line. If a high-to-low

transition does not occur on the ST pin within the watchdog

timeout period set by the TD pin (see Table 1), the RST and

RST pins will be asserted resulting in a microprocessor

reset. RST and RST will remain asserted for 250ms when

this occurs. A minimum pulse of 75ns or any transition high-

to-low on the ST pin will reset the watchdog timer. The

watchdog timer will be reset if ST sees a valid transition

within the watchdog timeout period.

tSD

ST

tTD

Watchdog Input

TD Pin

GND

Open

VCC

Min.

62.5ms

250ms

500ms

tTD

Typ.

150ms

600ms

1200ms

Max.

250ms

1000ms

2000ms

Table 1: Watchdog Timeout Period

Alternate Cross Reference Guide

Industry P/N

DS1232LP

DS1232LPS-2

DS1232

DS1232LPN

DS1232LPSN-2

DS1232N

MAX1232CPA

MAX1232CSA

MAX1232EPA

MAX1232ESA

MAX1232C/D

ILC Direct

Replacement

ILC1232N

ILC1232M

ILC1232N

ILC1232N

ILC1232M

ILC1232N

ILC1232N

ILC1232M

ILC1232N

ILC1232M

ILC1232D

Impala Linear Corporation

ILC1232 1.1

(408) 574-3939 www.impalalinear.com

June 1999 4

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