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20.3.5
CAN Node Control
Each CAN node may be configured and run independently of the other CAN node. Each
CAN node is equipped with its own node control logic to configure the global behavior
and to provide status information.
Note: In the following descriptions, index "x" stands for the node number and index "n"
represents the message object number.
Configuration Mode is activated when bit NCRx.CCE is set to 1. This mode allows CAN
bit timing parameters and the error counter registers to be modified.
CAN Analyze Mode is activated when bit NCRx.CALM is set to 1. In this operation mode,
Data And Remote Frames are monitored without active participation in any CAN transfer
(CAN transmit pin is held on recessive level). Incoming Remote Frames are stored in a
corresponding transmit message object, while arriving data frames are saved in a
matching receive message object.
In CAN Analyze Mode, the entire configuration information of the received frame is
stored in the corresponding message object, and can be evaluated by the CPU to
determine their identifier, XTD bit information and data length code (ID and DLC
optionally if the Remote Monitoring Mode is active, bit MOFCRn.RMM = 1). Incoming
frames are not acknowledged, and no Error Frames are generated. If CAN Analyze
Mode is enabled, Remote Frames are not responded to by the corresponding Data
Frame, and Data Frames cannot be transmitted by setting the transmit request bit
MOSTATn.TXRQ. Receive interrupts are generated in CAN Analyze Mode (if enabled)
for all error free received frames.
The node-specific interrupt configuration is also defined by the Node Control Logic via
the NCRx register bits TRIE, ALIE and LECIE:
•
If control bit TRIE is set to 1, a transfer interrupt is generated when the NSRx register
has been updated (after each successfully completed message transfer).
•
If control bit ALIE is set to 1, an error interrupt is generated when a "bus-off" condition
has been recognized or the Error Warning Level has been exceeded or under-run.
Additionally, list or object errors lead to this type of interrupt.
•
If control bit LECIE is set to 1, a last error code interrupt is generated when an error
code > 0 is written into bit field NSRx.LEC by hardware.
The Node x Status Register NSRx provides an overview about the current state of the
respective CAN node x, comprising information about CAN transfers, CAN node status,
and error conditions.
The CAN frame counter can be used to check the transfer sequence of message objects
or to obtain information about the instant a frame has been transmitted or received from
the associated CAN bus. CAN frame counting is performed by a 16-bit counter,
controlled by register NFCRx. Bit fields NFCRx.CFMOD and NFCRx.CFSEL determine
the operation mode and the trigger event incrementing the frame counter.
User's Manual
MultiCAN, V2.24
Controller Area Network Controller (MultiCAN)
20-21
TC1728
V1.0, 2011-12
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