SX28ACSLASHDP datasheet(19/51 Pages) PARALLAX

19 / 51 page

Parallax SX20AC/SX28AC

www.parallax.com

Page 19 of 51

Rev 1.6 11/20/2006

7.0

POWER DOWN MODE

The power down mode is entered by executing the

SLEEP instruction.

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

STATUS register.

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

transition edge. Setting a bit in the WKED_B register

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

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