SPSB081 datasheet(17/137 Pages) STMICROELECTRONICS

17 / 137 page

To prevent the system from a deadlock condition (no wake-up from standby possible) a configuration where all

wake-up is disabled, is not allowed.

Accordingly, if the following condition is set by SPI:

•

CAN_WU_EN = 0

•

LIN_WU_EN = 0

•

WU1_EN = 0

•

WU2_EN = 0

The effect is to put all these register bits in their default condition:

•

CAN_WU_EN = 1

•

LIN_WU_EN = 1

•

WU1_EN = 1

•

WU2_EN = 1

For SPSB081C devices (without LIN), at least one of these WU sources has to be kept (CAN, WU1 or WU2).

All wake-up sources are configured to default values in case of such invalid setting. The SPI error bit (SPIE) in the

global status register is set.

3.4.1

Wake-up inputs

The WU1 and WU2 inputs can be configured as wake-up sources. Each wake-up input is sensitive to any

level transition (positive and negative edge) and can be configured for static or cyclic monitoring of the input

voltage level by suitable setting of CR1 [8..11] bits (WUx_FILT_0 and WUx_FILT_1) which allows to choose the

monitoring among static, cyclic with timer 1 or cyclic with timer 2. When the configuration of a timer is changed,

the timer is automatically restarted using the new configuration.

For static contact monitoring, a filter time of tWU_STAT is implemented. The filter is started when the input voltage

passes the specified threshold VWUTHP. Wake-up status bit (WUx_STATE bit in SR5 [18..19]) is set only if this

threshold is passed for more than tWU_STAT.

Cyclic contact monitoring, conceived to reduce the quiescent current of the device, allows instead periodical (not

threshold dependent) activation of the wake-up input to read the status of the external contact. The periodical

activation is driven by timer 1 or timer 2 whose settings (on-time and period) can be configured through CR2

[8..13] and [16..21] bits (Tx_PER_y and Tx_ON_y bit). The input signal is filtered with a filter time of tWU_CYC

after a delay (80% of the configured timer on-time). A wake-up will be processed if the status has changed versus

the previous cycle, therefore wake-up status bit (WUx_STATE bit in SR5 [18..19]) is set only if status during

consecutive on-time is different, after the configured delay and tWU_CYC.

The buffered outputs OUT1, OUT2, OUT3, and OUT4 can be used to supply the external contacts with the timer

setting according to the cyclic monitoring of the wake-up input.

SPSB081

Wake-up from standby modes

DS14048 - Rev 3

page 17/137

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