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SX20AC/SX28AC

7.0 POWER DOWN MODE

The power down mode is entered by executing the

SLEEP instruction. Execution of the SLEEP instruction

causes the clock to the device to be stopped.
In power down mode, only the Watchdog Timer (WDT) is

active. If the Watchdog Timer is enabled, upon execution

of the SLEEP instruction, the Watchdog Timer is cleared,

the TO (time out) bit is set in the STATUS register, and

the PD (power down) bit is cleared in the STATUS regis-

ter.
There are three different ways to exit from the power

down mode: a timer overflow signal from the Watchdog

Timer (WDT), a valid transition on any of the Multi-Input

Wakeup pins (Port B pins), or through an external reset

input on the MCLR pin.
To achieve the lowest possible power consumption, the

Watchdog Timer should be disabled and the device

should exit the power down mode through the Multi-Input

Wakeup (MIWU) pins or an external reset.

7.1 Multi-Input Wakeup

Multi-Input Wakeup is one way of causing the device to

exit the power down mode. Port B is used to support this

feature. The WKEN_B register (Wakeup Enable Regis-

ter) allows any Port B pin or combination of pins to cause

the wakeup. Clearing a bit in the WKEN_B register

enables the wakeup on the corresponding Port B pin. If

multi-input wakeup is selected to cause a wakeup, the

trigger condition on the selected pin can be either rising

edge (low to high) or falling edge (high to low). The

WKED_B register (Wakeup Edge Select) selects the

desired transition edge. Setting a bit in the WKED_B reg-

ister selects the falling edge on the corresponding Port B.

Clearing the bit selects the rising edge. The WKEN_B

and WKED_B registers are set to FFh upon reset.
Once a valid transition occurs on the selected pin, the

WKPND_B register (Wakeup Pending Register) latches

the transition in the corresponding bit position. A logic `1'

indicates the occurrence of the selected trigger edge on

the corresponding Port B pin.
Upon exiting the power down mode, the Multi-Input

Wakeup logic causes program counter to branch to the

maximum program memory address (same as reset).
Figure 7-1 shows the Multi-Input Wakeup block diagram.

Figure 7-1. Multi-Input Wakeup Block Diagram

Internal Dat

a

Bus

MODE

Wake-up: Exit Power Down

RB7

RB6

RB1 RB0

WKED_B

WKPND_B

WKEN_B

MODE = 09

MODE = 0B

MODE = 0A

Port B

Configured

as Input

0 1

0 = Enable
1 = Disable