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r
19.2.4
Error Types
Bit Error
A CAN device which is currently transmitting also monitors
the bus. If the monitored bit value is different from the trans-
mitted bit value, a bit error is detected. However, the recep-
tion of a "dominant" bit instead of a "recessive" bit during the
transmission of a passive error flag, during the stuffed bit
stream of the arbitration field, or during the acknowledge
slot is not interpreted as a bit error.
Stuff Error
A stuff error is detected if 6 consecutive bits occur without a
state change in a message field encoded with bit stuffing.
Form Error
A form error is detected, if a fixed frame bit (e.g., CRC de-
limiter, ACK delimiter) does not have the specified value. For
External Reset or
Enable CR16CAN
Synchronize
Once the CAN module is enabled, it waits for 11 consecu-
tive recessive bits to synchronize with the bus. After that, the
CAN module becomes error active and can participate in
INTERFRAME SPACE
3
INT
SUSPEND
TRANSMIT
ANY FRAME
r
r
r
r
r
r
r
r
r
r
r
r
INT = Intermission
Suspend Transmission is only for error passive nodes.
Figure 42. Interframe Space
SYNC
11 consecutive 'recessive" bits
received
(TEC OR REC) > 95
ERROR
ACTIVE
(TEC AND REC) < 96
128 occurrences of
11 consecutive 'recessive" bits
Figure 43. Bus States
8
Bus Idle
r
r
r
r
r
r
r
r
r
a receiver, a "dominant" bit during the last bit of End of
Frame does not constitute a frame error.
Bit CRC Error
A CRC error is detected if the remainder from the CRC cal-
culation of a received CRC polynomial is non-zero.
Acknowledgment Error
An acknowledgment error is detected whenever a transmit-
ting node does not get an acknowledgment from any other
node (i.e., when the transmitter does not receive a "domi-
nant" bit during the ACK frame).
Error States
The device can be in one of five states with respect to error
handling (see Figure 43).
(TEC OR REC) > 127
ERROR
WARNING
(TEC AND REC) < 128
the bus communication. This state must also be entered af-
ter waking-up the device using the Multi-Input Wake-Up fea-
ture. See System Start-Up and Multi-Input Wake-Up on
page 140.
115
DATA FRAME OR
REMOTE FRAME
d
Note:
d = dominant
r = recessive
DS026
ERROR
PASSIVE
TEC > 255
BUS
OFF
DS027
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