AT89C51RE2 Atmel Corporation, AT89C51RE2 Datasheet - Page 118

• Manufacturer Part Number: AT89C51RE2
• Manufacturer: Atmel Corporation

Specifications of AT89C51RE2

• Flash (kbytes): 128 Kbytes
• Max. Operating Frequency: 60 MHz
• Cpu: 8051-12C
• Max I/o Pins: 34
• Spi: 1
• Uart: 2
• Sram (kbytes): 8.25
• Self Program Memory: API
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 4
• Isp: UART/OCD
• Watchdog: Yes

Power Management
Introduction
Idle Mode
Entering Idle Mode
Exiting Idle Mode
Power-Down Mode
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AT89C51RE2
Two power reduction modes are implemented in the AT89C51RE2. The Idle mode and the
Power-Down mode. These modes are detailed in the following sections. In addition to these
power reduction modes, the clocks of the core and peripherals can be dynamically divided by 2
using the X2 mode detailed in Section “Enhanced Features”, page 13.
Idle mode is a power reduction mode that reduces the power consumption. In this mode, pro-
gram execution halts. Idle mode freezes the clock to the CPU at known states while the
peripherals continue to be clocked. The CPU status before entering Idle mode is preserved, i.e.,
the program counter and program status word register retain their data for the duration of Idle
mode. The contents of the
Idle mode is detailed in Table 88.
To enter Idle mode, set the IDL bit in PCON register (see Table 89). The AT89C51RE2 enters
Idle mode upon execution of the instruction that sets IDL bit. The instruction that sets IDL bit is
the last instruction executed.
Note:
There are two ways to exit Idle mode:
1. Generate an enabled interrupt.
2. Generate a reset.
Note:
The Power-Down mode places the AT89C51RE2 in a very low power state. Power-Down mode
stops the oscillator, freezes all clock at known states. The CPU status prior to entering Power-
Down mode is preserved, i.e., the program counter, program status word register retain their
data for the duration of Power-Down mode. In addition, the
served. The status of the Port pins during Power-Down mode is detailed in Table 88.
Note:
–
–
If IDL bit and PD bit are set simultaneously, the AT89C51RE2 enters Power-Down mode. Then it
does not go in Idle mode when exiting Power-Down mode.
Hardware clears IDL bit in PCON register which restores the clock to the CPU.
Execution resumes with the interrupt service routine. Upon completion of the
interrupt service routine, program execution resumes with the instruction
immediately following the instruction that activated Idle mode. The general purpose
flags (GF1 and GF0 in PCON register) may be used to indicate whether an interrupt
occurred during normal operation or during Idle mode. When Idle mode is exited by
an interrupt, the interrupt service routine may examine GF1 and GF0.
A logic high on the RST pin clears IDL bit in PCON register directly and
asynchronously. This restores the clock to the CPU. Program execution momentarily
resumes with the instruction immediately following the instruction that activated the
Idle mode and may continue for a number of clock cycles before the internal reset
algorithm takes control. Reset initializes the AT89C51RE2 and vectors the CPU to
address C:0000h.
During the time that execution resumes, the internal RAM cannot be accessed; however, it is pos-
sible for the Port pins to be accessed. To avoid unexpected outputs at the Port pins, the instruction
immediately following the instruction that activated Idle mode should not write to a Port pin or to
the external RAM.
VCC may be reduced to as low as V
pation. Take care, however, that VDD is not reduced until Power-Down mode is invoked.
SFRs
and RAM are also retained. The status of the Port pins during
RET
during Power-Down mode to further reduce power dissi-
SFR
and RAM contents are pre-
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