33889 datasheet(32/60 Pages) FREESCALE

32 / 60 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

33889

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

Open wire detection operation:

Description:

The CANH and CANL open wire failures are not described

in the ISO document. Open wire is only diagnostic

information, as no CAN driver or receiver state will change in

case of an open wire condition.

In case one of the CAN wires are open, the communication

will continue through the remaining wire. In this situation the

MC33889 will receive information on one wire only and the

consequences are as follows:

when the bus is set in dominant:

- The differential receiver will toggle

- Only one of the single ended receivers CANH or of CANL

will toggle

The following figure illustrates the CAN signal during

normal communication and in the example of a CANH open

wire. The single ended receiver is sampled at the differential

receiver switching event, in a window of 1

µs.

Bus failure

identification

Description

Consequence on CAN driver

Consequence on Rx pin

no failure

default operation: CAN H and CANL driver active,

RTH and RTL termination switched ON

default operation: Report differential

receiver output

CANH open wire

default operation

CANH shorted to gnd

default operation

8, 3a

CANH shorted to Vdd

(5V)

CANH driver turn OFF. RTH termination switched

OFF

Rx report CANL single ended receiver

CANH shorted to Vbat

CANH driver turn OFF. RTH termination switched

OFF

Rx report CANL single ended receiver

CANL open wire

default operation

4, 7

CANL shorted to gnd or

CANL shorted to CANH

CANL driver is OFF. RTL termination switched

OFF

Rx report CANH single ended receiver

CANL shorted to Vdd (5V)

CANL driver is ON. RTL termination active

default operation

CANL shorted to Vbat

CANL driver is OFF. RTL termination switched

OFF

Rx report CANH single ended receiver

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