33903 datasheet(46/104 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33903/4/5

FUNCTIONAL DEVICE OPERATION

CYCLIC SENSE OPERATION DURING LP MODES

This function can be used in both LP Modes: VDD OFF and

VDD ON.

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

biasing of external contact switches. The contact switch state

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

Wake-Up from either 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 provides an opportunity to select a cyclic

sense period from 3.0 to 512 ms (selection in timer B).

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

duration of T_CSON (SPI selectable in INIT register, to 200 μs,

400

μs, 800 μs, or 1.6 ms). The I/O-0 HS transistor or LS

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

of I/O-0 prior to entering in LP Mode.

During the T-CSON duration, the I/O-x’s are monitored. If

one of them is high, the device will detect a Wake-Up.

(Figure 28).

Cyclic sense period is selected by the SPI configuration

prior to entering LP Mode. Upon entering LP Mode, the 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 typically 30

μs. This means that

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

than the deglitch time.

The diagram below (Figure 28) illustrates the cyclic sense

operation, with I/O-0 HS active and I/O-1 Wake-Up at high

level.

I/O-0

I/O-1

NORMAL MODE

LP MODE

I/O-0 HS active in Normal Mode

I/O-0 HS 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 200 us)

Wake-up event detected

I/O-0

I/O-1

S1 closed

S1 open

(typically 30 us)

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.

Figure 28. Cyclic Sense Operation - Switch to GND, Wake-up by Open Switch

33903 Datasheet(PDF) 46 Page - Freescale Semiconductor, Inc

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