AN2283 Freescale Semiconductor / Motorola, AN2283 Datasheet - Page 24

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

AN2283/D
Error Overview
24
NOTE:
Motorola Scalable Controller Area Network (MSCAN) Interrupts
Once again, the signals used in the CAN messages are stored in data
structures which mirror the MSCAN receive buffers so that when storing data
from the receive buffer all that is done is one for one data moves. In this case,
the variable structure is called Store_RX. This format provides an efficient
driver and improves execution time.
The MSCAN is designed to detect errors in transmission and reception of
messages, as specified in the Bosch CAN specification version 2.0. Methods
used to detect errors are:
When a node detects an error it transmits an error flag onto the CAN bus,
signaling all other nodes that a message error occurred. However, the host
CPU is NOT signaled when a specific error has occurred. These messages,
with error, are aborted and are retransmitted automatically.
The CAN nodes are able to distinguish between short disturbances and
permanent failures by tracking errors over a period of time. A CAN node is able
to determine whether the errors are due to faults of other nodes or itself and
takes the appropriate steps to confine its operations on the bus. A CAN node
can be in one of three states:
There are two counters that determine which state the node is in, the Transmit
Error Counter (TEC) and the Receive Error Counter (REC). The TEC is
associated with the node’s transmit state machine and the REC is associated
with the node’s receive state machine.
Both error counters must only be read when in Sleep or Soft_RESET.
In the Error Active state, both error counters are low so the node is fully able to
participate in bus communication and is able to send Active Error Flags upon
error detection at the node. The Error Passive state is entered when either error
counter reaches a higher level and the node’s communication on the bus
becomes restricted, sending Passive Error Flags upon error detection. If the
number of transmit errors of a node reaches an excessive level then the bus off
state is entered and the node’s communication on the bus is halted. The host
CPU will be signaled only when one of these state changes occurs at the node.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Bus Monitoring of what the MSCAN transmits
Cyclic Redundancy Check (CRC)
Message Frame Check
Error Active
Error Passive
Bus Off
Go to: www.freescale.com
MOTOROLA