AT89S2051 Atmel Corporation, AT89S2051 Datasheet - Page 8

• Manufacturer Part Number: AT89S2051
• Manufacturer: Atmel Corporation

Specifications of AT89S2051

• Flash (kbytes): 2 Kbytes
• Max. Operating Frequency: 24 MHz
• Cpu: 8051-12C
• Max I/o Pins: 15
• Uart: 1
• Sram (kbytes): 0.25
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 2
• Isp: SPI

10. Reset
10.1
Figure 10-1. Power-up and Brown-out Detection Sequence
8
Min V
Power-On Reset
BOD Level 2.3V
POR Level 1.4V
AT89S2051/S4051
CC
Level 2.7V
Internal
RESET
XTAL1
POR
BOD
V
0
CC
During reset, all I/O Registers are set to their initial values, the port pins are weakly pulled to
V
has three sources of reset: power-on reset, brown-out reset, and external 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 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
XTAL Oscillator Bypass fuse is OFF). Only after V
detection) level (see
2-ms delay after which the Internal Reset is deasserted and the microcontroller starts executing.
The built-in 2-ms delay allows the V
ing, thus guaranteeing the maximum operating clock frequency. The POR signal is activated
again, without any delay, when V
a cold reset) will set the POF flag in PCON. Refer to
behavior.
CC
, and the program starts execution from the Reset Vector, 0000H. The AT89S2051/S4051
(2 ms)
t
POR
CC
reaches the Power-on Reset threshold voltage, the Pierce Oscillator is enabled (if the
2.4V
Section 10.2 ”Brown-out
CC
(2 ms)
falls below the POR threshold level. A Power-On Reset (i.e.
t
CC
POR
voltage to reach the minimum 2.7V level before execut-
1.2V
Reset”), the BOD delay counter starts measuring a
CC
CC
is below the detection level. The POR cir-
Figure 10-1
has also reached the BOD (brown-out
for details on the POR/BOD
(2 ms)
t
POR
3390E–MICRO–6/08
t
t
t
t
t