mc33905s Freescale Semiconductor, Inc, mc33905s Datasheet - Page 51

• Manufacturer Part Number: mc33905s
• Description: System Basis Chip Gen2 With High Speed Can And Lin Interface
• Manufacturer: Freescale Semiconductor, Inc

thus a proper failure identification (requires 5 pulses on TXD).
The bus dominant clamp circuit will help to determine such
failure situation.
RX PERMANENT RECESSIVE FAILURE
hardware failure at the RX output pin and ensure that a
Implementation for Detection
low to high transition of the differential receiver. Excluding the
internal propagation delay, the RXD output should be low
when the differential receiver is low. In case of an external
short to VDD at the RXD output, RXD will be tied to a high
level and can be detected at the next low to high transition of
the differential receiver.
TXD PERMANENT DOMINANT
Principle
set into dominant level, and no communication is possible.
The device has a TXD permanent time out detector. After the
timeout, the bus driver is disabled and the bus is released into
a recessive state. The TXD permanent flag is set.
Analog Integrated Circuit Device Data
Freescale Semiconductor
RXD
The aim of this detection, is to diagnose an external
The implementation sense the RXD output voltage at each
If the TXD is set to a permanent low level, the CAN bus is
TXD
V
V DD
DD
Diag
/2
Rxsense
RX driver
Logic
CANL&H
RXD output
Diff output
RX flag
Diff
Figure 33. RX Path Simplified Schematic, RX Short to V
Figure 34. RX Path Simplified Schematic, Rx Short to V
RX flag latched
TX driver
Rx short to V DD
The RX flag is not the RXPR bit in the LPC register, and neither is the CANF in the INTR register.
V
DD
CANH
CANL
The RX flag is not the RXPR bit in the LPC register, and neither is the CANF in the INTR register.
60
Sampling
CANL&H
RXD output
RX no longer shorted to V DD
Prop delay
Diff output
RX flag
permanent failure at RX does not disturb the network
communication. If RX is shorted to a logic high signal, the
CAN protocol module within the MCU will not recognize any
incoming message. In addition it will not be able to easily
distinguish the bus idle state and can start communication at
any time. In order to prevent this, an RX failure detection is
necessary.
RXD driver is deactivated.
error is reported via SPI in CAN register.
Recovery Condition
level at TXD as shown in the following illustration.
Recovery
in case of a TXD short to RXD. The recovery condition for a
TXD permanent dominant (recovery means the re-activation
of the CAN drivers) is done by entering into a Normal Mode
controlled by the MCU or when TXD is recessive while RXD
change from recessive to dominant.
As soon as the RXD permanent recessive is detected, the
Once the error is detected the driver is disabled and the
The TXD permanent dominant is used and activated also
The internal recovery is done by sampling a correct low
Sampling
Sampling
DD
DD
RX short to V DD
Detection
Detection
CAN BUS FAULT DIAGNOSTIC
Sampling
RX flag latched
CAN INTERFACE
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