AT89LP51 Atmel Corporation, AT89LP51 Datasheet - Page 34

• 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

7.4
7.5
8. Power Saving Modes
8.1
34
Watchdog Reset
Software Reset
Idle Mode
AT89LP51/52
The AT89LP51/52 includes an on-chip Power-On Reset and Brown-out Detector circuit that
ensures that the device is reset from system power up. In most cases a RC startup circuit is not
required on the RST pin, reducing system cost, and the RST pin may be left unconnected if a
board-level reset is not present.
Note:
Figure 7-3.
When the Watchdog times out, it will generate a reset pulse lasting 49 clock cycles. By default
this pulse is also output on the RST pin. To disable the RST output the DISRTO bit in AUXR
(Compatibility mode) or WDTCON (Fast mode) must be set to one. Watchdog reset will set the
WDTOVF flag in WDTCON. To prevent a Watchdog reset, the watchdog reset sequence
1EH/E1H must be written to WDTRST before the Watchdog times out.
Watchdog Timer” on page 73.
The CPU may generate a 49-clock cycle reset pulse by writing the software reset sequence
5AH/A5H to the WDRST register. A software reset will set the SWRST bit in WDTCON. See
“Software Reset” on page 73
other than 5AH/A5H or 1EH/E1H to WDTRST will generate an immediate reset and set both
WDTOVF and SWRST to flag an error. Software reset will also drive the RST pin active unless
DISRTO is set.
The AT89LP51/52 supports two different power-reducing modes: Idle and Power-down. These
modes are accessed through the PCON register. Additional steps may be required to achieve
the lowest possible power consumption while using these modes.
Setting the IDL bit in PCON enters idle mode. Idle mode halts the internal CPU clock. The CPU
state is preserved in its entirety, including the RAM, stack pointer, program counter, program
status word, and accumulator. The Port pins hold the logic states they had at the time that Idle
was activated. Idle mode leaves the peripherals running in order to allow them to wake up the
WDT Reset
DISRTO
Internal Reset
RST also serves as the In-System Programming (ISP) enable. ISP is enabled when the external
reset pin is held active. When ISP is disabled by fuse, ISP may only be entered by pulling RST
active during power-up. If this behavior is necessary, it is recommended to use an active-low reset
so that ISP can be entered by shorting RST to GND at power-up.
Reset Pin Structure
V
CC
for details on the operation of the Watchdog.
for more information on software reset. Writing any sequences
POL = 1
RST
WDT Reset
DISRTO
Internal Reset
See “Programmable
V
CC
3709D–MICRO–12/11
POL = 0
RST