Configurations of this type are used in products

where the OFF switch is part of a keyboard

scanned by a micro which operates continuously

even in the OFF state.

Another application for the L4902A is supplying a

shadow-ram microcomputer chip (SGS M38SH72

for example)where a fast NV memory is backed up

on chip by a EEPROM when a low level on the reset

output occurs.

By adding two CMOS-SCHMIDT-TRIGGER and

few external components, also a watch dog func-

tion may be realized (see Figure 5). During normal

operation the microsystem supplies a periodical

pulse waveform;if an anomalousconditionoccours

(in the program or in the system), the pulses will be

absent and the disable input will be activated after

a settling time determined by R1 C1. In this condi-

abled, the system will be restarted with a new reset

front.

ing microprocessor malfunctioning.

Figure 4

Figure 5

L4902A

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