L9788 datasheet(151/264 Pages) STMICROELECTRONICS

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DS12308 Rev 4

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L9788

CAN FD interface

263

12.6.5

Smart reset RSTN effects

In order to avoid spurious interference on CAN Bus and false CAN error detection, during

the power-up sequence, as long the Smart Reset RSTN pin signal stays low the following

CAN configuration registers are masked to zero:



CAN_TX_EN (transmitter disabled);



CAN_TXD_DOM_EN (Dominant TxDC Time Out disabled);



CAN_PERM_REC_EN (CAN Permanent Recessive disabled);



CAN_PERM_DOM_EN (CAN Permanent Dominant disabled);



CAN_RXD_REC_EN (CAN RXDC Permanent Recessive disabled).

12.7

Wake up With U-Chip OFF

When the U-chip is off with CAN wake up option enabled (CAN_WAKEUP_EN = '1'), the

CAN transceiver can detect wake up activity on bus and then wake up the device. In this

situation the MSC bit WAKE_UP_CAN_DET is latched (MSC UPSTREAM READ 12,

Frame3). If the U-chip is off with CAN wake up option disabled (CAN_WAKEUP_EN = '0')

and automatic voltage biasing disabled (CAN_AUTO_BIAS = '0') the transceiver goes in

Sleep mode. Otherwise if the U-chip is off with CAN wake up option disabled

(CAN_WAKEUP_EN = '0') and automatic voltage biasing enabled (CAN_AUTO_BIAS = '1')

the transceiver goes in CAN_BIAS_OFF state and after a period greater than Tsilence

without activity on bus goes in Sleep mode.

12.8

Wake up with U-Chip ON

When the U-chip is on and the CAN transceiver is in low power mode (CAN_EN bit = '0')

and the wake up option is enabled (CAN_WAKEUP_EN = '1'), the CAN Transceiver can

detect wake up activity on bus. In this situation the MSC bit WAKE_UP_CAN_DET_AUTO is

latched (MSC UPSTREAM READ 13, Frame3) and a dominant pulse of tdom_pulse is sent on

pad CAN_RX. If the CAN_AUTO_BIAS bit MSC_CONFIG_REG21[7] is set and the CAN

transceiver is in the state CAN_STBY_ON the detection of a wake up activity will bring the

transceiver in the state CAN_BIAS_ON

12.8.1

Wake up options

For the wake up feature the device logic differentiates different Wake-up detection

conditions.

12.8.2

Normal pattern wake up

Normal pattern wake up can occur when CAN pattern wake up option is enabled

(CAN_PATTERN_EN = '1'), the wake up enable bit is set (CAN_WAKEUP_EN = '1') and the

CAN transceiver is in low-power mode. In order to have a Wake-up detection, the following

criteria must be fulfilled:



The CAN interface wake up receiver must receive a series of two consecutive valid

dominant pulses, each of which must be longer than tfilter;



The distance between 2 pulses must be longer than tfilter;



The two pulses must occur within a time frame of twake.

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