AT89C51AC2 datasheet(20/121 Pages) ATMEL

20 / 121 page

A/T89C51AC2

4127G–8051–05/06

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.

Generate a reset.

–

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 T89C51CC02 and vectors the CPU to address C:0000h.

Notes:

1. During the time that execution resumes, the internal RAM cannot be accessed; how-

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.

2. If Idle mode is invoked by ADC Idle, the ADC conversion completion will exit Idle.

Power-down Mode

The Power-down mode places the T89C51CC02 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.

Entering Power-down Mode

To enter Power-down mode, set PD bit in PCON register. The T89C51CC02 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.

Exiting Power-down Mode

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:

Generate an enabled external interrupt.

–

The T89C51CC02 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.

Note:

1. The external interrupt used to exit Power-down mode must be configured as level

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.

2. Exit from power-down by external interrupt does not affect the SFRs nor the internal

RAM content.

AT89C51AC2 Datasheet(PDF) 20 Page - ATMEL Corporation

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