STC12LE5616AD datasheet(41/377 Pages) STC

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2.2.3 Stop / Power Down (PD) Mode and Demo Program (C and ASM)

An instruction that sets PD/PCON.1 cause that to be the last instruction executed before going into the Power-

Down mode. In the Power-Down mode, the on-chip oscillator and the Flash memory are stopped in order to

minimize power consumption. Only the power-on circuitry will continue to draw power during Power-Down.

The contents of on-chip RAM and SFRs are maintained. The power-down mode can be woken-up by RESET

pin, external interrupt INT0 ~ INT1, RXD pin, T0 pin, T1 pin and PCA input pins—PWM pins and PWM pins.

When it is woken-up by RESET, the program will execute from the address 0x0000. Be carefully to keep RESET

pin active for at least 10ms in order for a stable clock. If it is woken-up from I/O, the CPU will rework through

jumping to related interrupt service routine. Before the CPU rework, the clock is blocked and counted until 32768

in order for denouncing the unstable clock. To use I/O wake-up, interrupt-related registers have to be enabled

and programmed accurately before power-down is entered. Pay attention to have at least one “NOP” instruction

subsequent to the power-down instruction if I/O wake-up is used. When terminating Power-down by an interrupt,

the wake up period is internally timed. At the negative edge on the interrupt pin, Power-Down is exited, the

oscillator is restarted, and an internal timer begins counting. The internal clock will be allowed to propagate and

the CPU will not resume execution until after the timer has reached internal counter full. After the timeout period,

the interrupt service routine will begin. To prevent the interrupt from re-triggering, the interrupt service routine

should disable the interrupt before returning. The interrupt pin should be held low until the device has timed out

and begun executing. The user should not attempt to enter (or re-enter) the power-down mode for a minimum of 4

us until after one of the following conditions has occured: Start of code execution(after any type of reset), or Exit

from power-down mode.

I/O

INTx

0.1uF

5MΩ

The following circuit can timing wake up MCU from power down mode when external interrupt sources do not

exist

Operation step:

1. I/O ports are first configured to push-pull output(strong pull-up) mode

2. Writen 1s into ports I/O ports

3. the above circuit will charge the capacitor C1

4. Writen 0s into ports I/O ports, MCU will go into power-down mode

5. The above circuit will discharge. When the electricity of capacitor C1 has been discharged less than

0.8V, external interrupt INTx pin will generate a falling edge and wake up MCU from power-down

mode automatically.

300Ω

STC12LE5616AD Datasheet(PDF) 41 Page - STCmicro Technology Co,.Ltd