Rainbow Electronics CAN интерфейс - Manual (Page 26)

BOSCH
ROBERT BOSCH GmbH, Postfach 50, D-7000 Stuttgart 1
Sep. 1991
Part A - page 24
7 FAULT CONFINEMENT
With respect to fault confinement a unit may be in one of three states:
• ’error active’
• ’error passive’
• ’bus off’
An ’error active’ unit can normally take part in bus communication and sends an
ACTIVE ERROR FLAG when an error has been detected.
An ’error passive’ unit must not send an ACTIVE ERROR FLAG. It takes part in bus
communication but when an error has been detected only a PASSIVE ERROR FLAG is
sent. Also after a transmission, an ’error passive’ unit will wait before initiating a further
transmission. (See SUSPEND TRANSMISSION)
A ’bus off’ unit is not allowed to have any influence on the bus. (E.g. output drivers
switched off.)
For fault confinement two counts are implemented in every bus unit:
1) TRANSMIT ERROR COUNT
2) RECEIVE ERROR COUNT
These counts are modified according to the following rules:
(note that more than one rule may apply during a given message transfer)
1. When a RECEIVER detects an error, the RECEIVE ERROR COUNT will be
increased by 1, except when the detected error was a BIT ERROR during the
sending of an ACTIVE ERROR FLAG or an OVERLOAD FLAG.
2. When a RECEIVER detects a ’dominant’ bit as the first bit after sending an ERROR
FLAG the RECEIVE ERROR COUNT will be increased by 8.
3. When a TRANSMITTER sends an ERROR FLAG the TRANSMIT ERROR COUNT
is increased by 8.
Exception 1:
If the TRANSMITTER is ’error passive’ and detects an ACKNOWLEDGMENT
Fault Confinement