at89s8253-24psu ATMEL Corporation, at89s8253-24psu Datasheet - Page 11

• Manufacturer Part Number: at89s8253-24psu
• Description: At89s8253 8-bit Microcontroller With 12k Bytes Flash And 2k Bytes Eeprom
• Manufacturer: ATMEL Corporation

7. Power-On Reset
Figure 7-1.
7.1
3286K–MICRO–12/06
Min V
Brown-out Reset
BOD Level 2.3V
POR Level 1.4V
CC
Level 2.7V
Internal
RESET
XTAL1
Power-up and Brown-out Detection Sequence
POR
BOD
V
0
CC
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 V
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 V
how long the device is kept in POR after V
again, without any delay, when V
a cold reset) will set the POF flag in PCON.
The AT89S8253 has an on-chip Brown-out Detection (BOD) circuit for monitoring the V
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 V
cuting at speed, the system will gracefully enter reset without the possibility of errors induced by
incorrect execution. When V
is immediately activated. When V
starts the MCU after the timeout period has expired in approximately 2 ms.
(2 ms)
t
POR
CC
reaches the Power-on Reset threshold voltage, the POR delay counter determines
2.4V
CC
decreases to a value below the trigger level, the Brown-out Reset
CC
CC
falls below the POR threshold level. A Power-On Reset (i.e.
increases above the trigger level, the BOD delay counter
1.2V
CC
rise, nominally 2 ms. The POR signal is activated
CC
is below the detection level. The POR cir-
(2 ms)
CC
t
fails or dips while exe-
POR
AT89S8253
t
t
t
t
t
CC
level
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