33905 datasheet(39/91 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33904/5

FUNCTIONAL DEVICE OPERATION

CYCLIC SENSE OPERATION DURING LP MODES

This function can be used in both Low Power modes (LP

Vdd off and LP Vdd on).

Cyclic sense is the periodic activation of I/O-0, to allow

biasing of external contact swicthes. The contact switch state

can be detected via I/O-1, 2 and 3, and device can wake up

from LP mode.

Cyclic sense is optimized and designed primarily for

closed contact switch, in order to minimize consumption via

the contact pull up resistor.

Principle:

A dedicated timer allows to select a cyclic sense period

from 3 to 512ms (selection in timer B).

At end of the period, the I/O-0 will be activated for a

duration of T_cson (SPI selectable in INIT register, to 200us,

400us, 800us or 1.6ms). The I/O-0 high side transistor or low

side transistor can be activated. The selection is done by the

state of I/O-0 prior to enter in low power mode.

During the T-cson duration, the I/O-x are monitored. If one

of them is high, the device will detect a wake up. (Figure 21).

Cyclic sense period is selected by SPI configuration prior

to enter in device low power mode. Upon entering LP mode, I/

O-0 should be activated.

The level of I/O-1 is sense during the I/O-0 active time,

and is deglitched for a duration of typ 30us. This mean that I/

O-1 should be in the expected state for a duration longer than

the deglitcher time.

The diagram below (Figure 21) illustrates the cyclic sense

operation, with I/O-0 high side active and I/O-1 wake up in

case of high level.

Figure 21. Cyclic Sense operation - switch to gnd, wake up by open switch

I/O-0

I/O-1

NORMAL MODE

LOW POWER MODE

I/O-0 high side active in Normal mode

I/O-0 high side active during cyclic sense active time

Cyclic sense period

Cyclic sense active time

RESET or NORMAL REQUEST MODE

Wake up detected.

state of I/O-1 low => no wake up

Cyclic sense active

I/O-1 deglitcher time

I/O-1 high => wake up

I/O-0

I/O-1

Zoom

time (ex 200us)

Wake up event detected

I/O-0

I/O-1

S1 closed

S1 open

(typ 30us)

I/O-2

I/O-3

I/O-0

I/O-1

I/O-2

I/O-3

Upon entering in LP mode, all 3

contact switches are closed.

In LP mode, 1 contact switch is open.

High level is detected on I/O-x, and device wakes up.

33905 Datasheet(PDF) 39 Page - Freescale Semiconductor, Inc

33905 Datasheet(HTML) 39 Page - Freescale Semiconductor, Inc

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