AT89LP51 Atmel Corporation, AT89LP51 Datasheet - Page 32

• Manufacturer Part Number: AT89LP51
• Manufacturer: Atmel Corporation

Specifications of AT89LP51

• Flash (kbytes): 4 Kbytes
• Max. Operating Frequency: 20 MHz
• Cpu: 8051-1C
• Max I/o Pins: 36
• Uart: 1
• Sram (kbytes): 0.25
• Eeprom (bytes): 256
• Self Program Memory: IAP
• Operating Voltage (vcc): 2.4 to 5.5
• Timers: 3
• Isp: SPI
• Watchdog: Yes

7. Reset
7.1
32
Power-on Reset
AT89LP51/52
During reset, all I/O Registers are set to their initial values, the port pins are set to their default
mode, and the program starts execution from the Reset Vector, 0000H. The AT89LP51/52 has
five sources of reset: power-on reset, brown-out reset, external reset, watchdog reset, and soft-
ware reset.
A Power-on Reset (POR) is generated by an on-chip detection circuit. The detection level V
is nominally 1.4V. The POR is activated whenever V
cuit can be used to trigger the start-up reset or to detect a major supply voltage failure. The POR
circuit ensures that the device is reset from power-on. A power-on sequence is shown in
7-1. When V
lasting t
how long the device is kept in POR after V
until after V
activated again, without any delay, when V
Reset (i.e. a cold reset) will set the POF flag in PCON. The internally generated reset can be
extended beyond the power-on period by holding the RST pin active longer than the time-out.
Figure 7-1.
Note:
The start-up timer delay is user-configurable with the Start-up Time User Fuses and depends on
the clock source
after a Brown-out Reset or when waking up from Power-down during internally timed mode. The
start-up delay should be selected to provide enough settling time for V
source. The device operating environment (supply voltage, frequency, temperature, etc.) must
meet the minimum system requirements before the device exits reset and starts normal opera-
tion. The RST pin may be held active externally until these conditions are met.
POR
t
POR
Time-out
DD
is started. When the initialization sequence completes, the start-up timer determines
Internal
Internal
is approximately 143 µs ± 5%.
DD
Reset
Reset
reaches the Brown-out Detector (BOD) threshold voltage V
Power-on Reset Sequence
POL
RST
RST
V
reaches the Power-on Reset threshold voltage V
(Table
DD
t
POR
7-1). The Start-Up Time fuses also control the length of the start-up time
V
POR
V
BOD
(RST Controlled Externally)
DD
DD
t
SUT
falls below the POR threshold level. A Power-on
rise. The start-up timer does not begin counting
DD
(POL Tied to VCC)
(RST Tied to GND)
is below the detection level. The POR cir-
POR
, an initialization sequence
DD
V
IL
BOD
and the selected clock
t
RHD
. The POR signal is
3709D–MICRO–12/11
Figure
POR