T89C51CC01 Atmel, T89C51CC01 Datasheet - Page 23

• Manufacturer Part Number: T89C51CC01
• Description: Enhanced 8-Bit Microcontroller
• Manufacturer: Atmel

Power-down Mode
Entering Power-down Mode
Exiting Power-down Mode
4129K–CAN–01/05
2. Generate a reset.
Note:
The Power-down mode places the T89C51CC01 in a very low power state. Power-down
mode stops the oscillator and freezes all clocks 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
SFRs and RAM contents are preserved. The status of the Port pins during Power-down
mode is detailed in Table 14.
To enter Power-down mode, set PD bit in PCON register. The T89C51CC01 enters the
Power-down mode upon execution of the instruction that sets PD bit. The instruction
that sets PD bit is the last instruction executed.
If VDD was reduced during the Power-down mode, do not exit Power-down mode until
VDD is restored to the normal operating level.
There are two ways to exit the Power-down mode:
1. Generate an enabled external interrupt.
Note:
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–
1. During the time that execution resumes, the internal RAM cannot be accessed; how-
2. If Idle mode is invoked by ADC Idle, the ADC conversion completion will exit Idle.
1. The external interrupt used to exit Power-down mode must be configured as level
2. Exit from power-down by external interrupt does not affect the SFRs nor the internal
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 T89C51CC01 and vectors the CPU to address C:0000h.
The T89C51CC01 provides capability to exit from Power-down using INT0#,
INT1#.
Hardware clears PD bit in PCON register which starts the oscillator and
restores the clocks to the CPU and peripherals. Using INTx# input,
execution resumes when the input is released (see Figure 9) while using
KINx input, execution resumes after counting 1024 clock ensuring the
oscillator is restarted properly (see Figure 8). 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 Power-down mode.
ever, it is possible 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.
sensitive (INT0# and INT1#) and must be assigned the highest priority. In addition,
the duration of the interrupt must be long enough to allow the oscillator to stabilize.
The execution will only resume when the interrupt is deasserted.
RAM content.
T89C51CC01
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