AT89S8253-24SC View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT89S8253-24SC

8-bit Microcontroller with 12K Bytes Flash and 2K Bytes EEPROM

Atmel Corporation 

AT89S8253

7. Power-On Reset

A Power-On Reset (POR) is generated by an on-chip detection circuit. The detection level is

nominally 1.4V. The POR is activated whenever VCC is below the detection level. The POR cir-

cuit can be used to trigger the start-up reset or to detect a supply voltage failure in devices

without a brown-out detector. The POR circuit ensures that the device is reset from power-on.

When VCC reaches the Power-on Reset threshold voltage, the POR delay counter determines

how long the device is kept in POR after VCC rise, nominally 2 ms. The POR signal is activated

again, without any delay, when VCC falls below the POR threshold level. A Power-On Reset (i.e.

a cold reset) will set the POF flag in PCON.

Figure 7-1. Power-up and Brown-out Detection Sequence

VCC

Min VCC Level 2.7V

BOD Level 2.3V

POR Level 1.4V

t

POR

XTAL1

2.4V

BOD

Internal

RESET

0

tPOR

(2 ms)

1.2V

t

t

t

tPOR

(2 ms)

t

7.1 Brown-out Reset

The AT89S8253 has an on-chip Brown-out Detection (BOD) circuit for monitoring the VCC level

during operation by comparing it to a fixed trigger level of 2.4V (max). The trigger level for the

BOD is nominally 2.2V. The purpose of the BOD is to ensure that if VCC fails or dips while exe-

cuting at speed, the system will gracefully enter reset without the possibility of errors induced by

incorrect execution. When VCC decreases to a value below the trigger level, the Brown-out Reset

is immediately activated. When VCC increases above the trigger level, the BOD delay counter

starts the MCU after the timeout period has expired in approximately 2 ms.

11

3286H–MICRO–9/05

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