Power Monitor

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

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

RST

PBRST

RST

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.

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.

TD Pin

Min.

Typ.

Max.

GND

62.5ms

150ms

250ms

Open

250ms

600ms

1000ms

500ms

1200ms

2000ms

Industry P/N

ILC Direct

Replacement

DS1232LP

ILC1232N

DS1232LPS-2

ILC1232M

DS1232

ILC1232N

DS1232LPN

ILC1232N

DS1232LPSN-2

ILC1232M

DS1232N

ILC1232N

MAX1232CPA

ILC1232N

MAX1232CSA

ILC1232M

MAX1232EPA

ILC1232N

MAX1232ESA

ILC1232M

MAX1232C/D

ILC1232D

RST

RST

ST

ILC1232 mP Supervisory Circuit

Sept 1999

Circuit Decription

Power-Up/Power-Down Sequence

Pushbutton Reset

Watchdog Input

Table 1: Watchdog Timeout Period

Alternate Cross Reference Guide

Impala Linear Corporation

4

(408) 574-3939

www.impalalinear.com

ILC1232 1.1

June 1999