MC68HC08AS32 Datasheet, PDF (333/394 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

Byte Data Link Controller-Digital (BDLC-D)
BDLC MUX Interface
CRC — Cyclical Redundancy Check Byte
This byte is used by the receiver(s) of each message to determine if
any errors have occurred during the transmission of the message.
The BDLC calculates the CRC byte and appends it onto any
messages transmitted onto the J1850 bus. It also performs CRC
detection on any messages it receives from the J1850 bus.
CRC generation uses the divisor polynomial X⁸ + X⁴ + X³ + X² + 1.
The remainder polynomial initially is set to all ones. Each byte in the
message after the start of frame (SOF) symbol is processed serially
through the CRC generation circuitry. The one’s complement of the
remainder then becomes the 8-bit CRC byte, which is appended to
the message after the data bytes in MSB-to-LSB order.
When receiving a message, the BDLC uses the same divisor
polynomial. All data bytes, excluding the SOF and end of data
symbols (EOD) but including the CRC byte, are used to check the
CRC. If the message is error free, the remainder polynomial will equal
X⁷ + X⁶ + X² = $C4, regardless of the data contained in the message.
If the calculated CRC does not equal $C4, the BDLC will recognize
this as a CRC error and set the CRC error flag in the BSVR.
EOD — End-of-Data Symbol
The EOD symbol is a long 200-µs passive period on the J1850 bus
used to signify to any recipients of a message that the transmission
by the originator has completed. No flag is set upon reception of the
EOD symbol.
IFR — In-Frame Response Bytes
The IFR section of the J1850 message format is optional. Users
desiring further definition of in-frame response should review the SAE
J1850 — Class B Data Communications Network Interface
specification.
EOF — End-of-Frame Symbol
This symbol is a long 280-µs passive period on the J1850 bus and is
longer than an end-of-data (EOD) symbol, which signifies the end of
a message. Since an EOF symbol is longer than a 200-µs EOD
MC68HC08AS32 — Rev. 3.0
MOTOROLA
Byte Data Link Controller-Digital (BDLC-D)
Advance Information
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