cop87l84bc National Semiconductor Corporation, cop87l84bc Datasheet - Page 32

• Manufacturer Part Number: cop87l84bc
• Description: 8-bit Cmos Otp Microcontrollers With 16k Memory, Comparators, And Can Interface
• Manufacturer: National Semiconductor Corporation

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Frame Formats
module 1 = error active receiver with a local fault at t1
module 2 = error passive transmitter detects bit error at t2
module 3 = error passive receiver detects stuff error at t2
The following errors can be detected:
A CAN device that is sending also monitors the bus. If the
monitored bit value is different from the bit value that is sent,
a bit error is detected. The reception of a “dominant” bit in-
stead of a “recessive” bit during the transmission of a pas-
sive error flag, during the stuffed bit stream of the arbitration
field or during the acknowledge slot, is not interpreted as a
bit error.
A stuff error is detected, if the bit level after 6 consecutive bit
times has not changed in a message field that has to be
coded according to the bit stuffing method.
A form error is detected, if a fixed frame bit (e.g., CRC delim-
iter, ACK delimiter) does not have the specified value. For a
receiver a “dominant” bit during the last bit of End of Frame
does NOT constitute a form error.
• Bit Error
• Stuff error
• Form Error
• Bit CRC Error
(Continued)
FIGURE 29. Order of Bit Transmission within a CAN Frame
FIGURE 28. Error Frame — Error Passive Transmitter
32
A CRC error is detected if the remainder of the CRC calcula-
tion of a received CRC polynomial is non-zero.
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).
The device can be in one of three states with respect to error
handling:
An error active unit can participate in bus communication
and sends an active (“dominant”) error flag.
• Acknowledgment Error
• Error active
• Error passive
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