© 2004 Microchip Technology Inc. DS70074C-page 26-17
Section 26. Appendix
Appendix
26
The error detection mechanisms have the following properties:
• all global errors are detected
• all local errors at transmitters are detected
• up to 5 randomly distributed errors in a message are detected
• burst errors of length less than 15 in a message are detected
• errors of any odd number in a message are detected
14. Error Signalling and Recovery Time – Corrupted messages are flagged by any node
detecting an error. Such messages are aborted and will be retransmitted automatically.
The recovery time from detecting an error until the start of the next message is at most 31
bit times, if there is no further error.
15. Fault Confinement – CAN nodes are able to distinguish short disturbances from
permanent failures. Defective nodes are switched off.
16. Connections – The CAN serial communication link is a bus to which a number of units may
be connected. This number has no theoretical limit. Practically the total number of units
will be limited by delay times and/or electrical loads on the bus line.
17. Single Channel – The bus consists of a single channel that carries bits. From this data
resynchronization, information can be derived. The way in which this channel is
implemented is not fixed in this specification (i.e., single wire (plus ground), two differential
wires, optical fires, etc).
18. Bus values – The bus can have one of two complementary logical values; ‘dominant’ or
‘recessive’. During simultaneous transmission of ‘dominant’ and ‘recessive’ bits, the
resulting bus value will be ‘dominant’. For example, in case of a wired-AND
implementation of the bus, the ‘dominant’ level would be represented by a logical ‘0’ and
the ‘recessive’ level by a logical ‘1’. Physical states (e.g., electrical voltage, light) that
represent the logical levels are not given in the specification.
19. Acknowledgment – All receivers check the consistency of the message being received
and will acknowledge a consistent message and flag an inconsistent message.
20. Sleep Mode; Wake-up – To reduce the system's power consumption, a CAN device may
be set into Sleep mode without any internal activity and with disconnected bus drivers.
The Sleep mode is finished with a wake-up by any bus activity or by internal conditions of
the system. On wake-up, the internal activity is restarted, although the MAC sub-layer will
be waiting for the system's oscillator to stabilize and it will then wait until it has
synchronized itself to the bus activity (by checking for eleven consecutive ‘recessive’ bits),
before the bus drivers are set to “on-bus” again.
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