70353C Datasheet, PDF (7/76 Pages) Microchip Technology – Section 21. Enhanced Controller Area Network

Section 21. Enhanced Controller Area Network (ECAN™)
21.2.4 Error Frame
An error frame is generated by any node that detects a bus error. An error frame consists of an
Error Flag field followed by an Error Delimiter field. The Error Delimiter consists of eight recessive
bits and allows the bus nodes to restart communication correctly after an error has occurred.
There are two types of Error Flag fields, depending on the error status of the node that detects
the error:
• Error Active Flag – contains six consecutive dominant bits, which forces all other nodes
on the network to generate Error Echo Flags, thereby resulting in a series of 6-12 dominant
bits on the bus.
• Error Passive Flag – contains six consecutive recessive bits, with the result that unless
the bus error is detected by the transmitting node, the transmission of an Error Passive flag
will not affect the communications of any other node on the network.
21.2.5 Overload Frame
An Overload Frame can be generated by a node either when a dominant bit is detected during
Interframe Space or when a node is not ready to receive the next message (for example, if it is
still reading the previous received message). An Overload Frame has the same format as an
Error Frame with an Active Error Flag, but can only be generated during Interframe Space. It
consists of an Overload Flag field with six dominant bits followed by an Overload Delimiter field
with eight recessive bits. A node can generate a maximum of two sequential Overload Frames
to delay the start of the next message.
21.2.6 Interframe Space
The Interframe Space separates the successive frames being transmitted on the CAN bus. It
consists of at least three recessive bits, referred to as Intermission. The Interframe Space allows
nodes time to internally process the previously received message before the start of the next
frame. If the transmitting node is in the Error Passive state, additional eight recessive bits will be
inserted in the Interframe Space before any other message is transmitted by the node. The
additional eight recessive bits (also referred to as, Suspend Transmit field) allow time for other
transmitting nodes to take control of the bus.
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DS70353C-page 21-7