33889 Datasheet, PDF (32/60 Pages) Freescale Semiconductor, Inc – System Basis Chip with Low Speed Fault Tolerant CAN Interface

FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
Bus failure
identification
Description
Consequence on CAN driver
Consequence on Rx pin
1
5
8, 3a
3
2
4, 7
9
6
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
default operation
CANH shorted to gnd
default operation
default operation
CANH shorted to Vdd
(5V)
CANH driver turn OFF. RTH termination switched Rx report CANL single ended receiver
OFF
CANH shorted to Vbat
CANH driver turn OFF. RTH termination switched Rx report CANL single ended receiver
OFF
CANL open wire
default operation
default operation
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
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 1µs.
33889
32
Analog Integrated Circuit Device Data
Freescale Semiconductor