L9779WD datasheet(96/170 Pages) STMICROELECTRONICS

96 / 170 page

Functional description

L9779WD

96/170

DocID027452 Rev 5

CAN error handling

The L9779WD provides the following 4 error handling features that are realized in different

stand alone CAN transceivers / micro controllers to switch the application back to normal

operation mode.

If one of the below fault happens the status bit CAN_ERROR is set.

The error handling features can be disabled through the CAN_ERR_DIS bit.

Dominant CAN_TX time out

If CAN_TX is in dominant state (low) for t > tdom (TxD) the transmitter will be disabled,

status bit will be latched and can be read and cleared by MSC. The transmitter remains

disabled until the status register is cleared.

CAN permanent recessive

If CAN_TX changes to dominant (low) state but CAN bus (CAN_RX pin) does not

follow for 4 times, the transmitter will be disabled, status bit will be latched and can be

read and cleared by MSC. The transmitter remains disabled until the status register is

cleared.

CAN permanent dominant

If the CAN bus state is dominant (low) for t > tCAN a permanent dominant status will be

detected. The status bit will be latched and can be read and cleared by MSC. The

transmitter will not be disabled.

CAN_RX permanent recessive

If CAN_RX pin is clamped to recessive (high) state, the controller is not able to

recognize a bus dominant state and could start messages at any time, which results in

disturbing the overall bus communication.

Therefore, if RX_ECHO does not follow CAN_TX for 4 times the transmitter will be

disabled. The status bit will be latched and can be read and optionally cleared by MSC.

The transmitter remains disabled until the status register is cleared.

CAN transceiver electrical characteristics

Table 42. CAN transceiver electrical characteristics

Symbol

Description

Test conditions

Min

Typ

Max

Unit

CAN_TX

VTX_CANLOW

Input voltage

dominant level

Active mode

-0.3

1.1

VTX_CANHIGH

Input voltage

recessive level

Active mode

2.3

VDD

+0.3

VTX_CANHYS

VTX_CANHIGH-

VTX_CANLOW

Active mode

0.25

0.5

RTX_CANPU

CAN_TX pull up

resistor

Active Mode

250

kΩ

CAN_RX

VRX_CANLOW

Output voltage

dominant level

Active mode,

VDD_IO = 5 V or 3.3 V, 2 mA

0.5

VRX_CANHIGH

Output voltage

recessive level

VDD_IO

-0.5

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