AN2283 Freescale Semiconductor / Motorola, AN2283 Datasheet - Page 26

• Manufacturer Part Number: AN2283
• Description: Scalable Controller Area Network (MSCAN)
• Manufacturer: Freescale Semiconductor / Motorola

AN2283/D
Error Signaling
Active Error Flag
Passive Error Flag
Fault Confinement
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OF FRAME
START
ARBITRATION
FIELD
CONTROL
FIELD
Motorola Scalable Controller Area Network (MSCAN) Interrupts
When a node detects an error in transmission or reception, it signals the bus by
transmitting an Error Flag. There are two kinds of error flags:
These flags correspond to the error state of a node, which is governed by
transmit and receive error counters. A node can be Error Active or Error
Passive depending on these counters. When an Error Active Node detects an
error condition, the node signals this by transmitting an Active Error Flag. When
a Error Passive Node detects an error condition, the node signals this by
transmitting a Passive Error Flag.
An Active Error Flag consists of six consecutive dominant [0] bits which:
When a node sends out an Active Error Flag after detecting an error, all the
other nodes detect an error condition also and start to transmit their own Error
Flags. So, a sequence of dominant [0] bits results from the overlaying of
different error flag transmitted by individual nodes. As a result, the total length
of the sequence varies between a minimum of 6 and a maximum of 12.
The Passive Error Flag consists of six recessive [1] consecutive bits that do not
overwrite other bits. A Passive Error Flag that is transmitted while any dominant
bits are present on the bus will not be seen by any other nodes on the bus,
including the transmitter.
Fault Confinement is a method for discriminating between temporary errors
and permanent failures. Nodes that constantly generate errors are prevented
from disturbing communication between error free nodes. To do this, each
node has a Transmit Error Counter (TEC) and a Receive Error Counter (REC).
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Freescale Semiconductor, Inc.
For More Information On This Product,
Active Error Flag
Passive Error Flag
Overwrite other bits on the bus and break the rule of bit stuffing, or
Destroy the ACK field or EOF field
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Figure 19. Data Frame
FIELD
DATA
FIELD
CRC
ACKNOWLEDGE FIELD
SLOT
ACK
FIELD
ACK
DELIMITER
MOTOROLA
ACK
OF FRAME
END