mc68hc705v12 Freescale Semiconductor, Inc, mc68hc705v12 Datasheet - Page 149

• Manufacturer Part Number: mc68hc705v12
• Description: M68hc05-based Mcu Hc05 Freescale Semiconductor
• Manufacturer: Freescale Semiconductor, Inc

MC68HC705V12
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Rev. 3.0
CRC — Cyclical Redundancy Check Byte
EOD — End-of-Data Symbol
IFR — In-Frame Response Bytes
EOF — End-of-Frame Symbol
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 X
The remainder polynomial initially is set to all 1s. 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
X
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.
The EOD symbol is a long 200- s 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.
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.
This symbol is a long 280- s 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- s EOD
Freescale Semiconductor, Inc.
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Byte Data Link Controller – Digital (BDLC–D)
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= $C4, regardless of the data contained in the message.
Byte Data Link Controller – Digital (BDLC–D)
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BDLC MUX Interface
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Advance Information
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+ 1.