MC68HC08AS32 Datasheet, PDF (332/394 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

Byte Data Link Controller-Digital (BDLC-D)
20.5.2 J1850 Frame Format
All messages transmitted on the J1850 bus are structured using the
format shown in Figure 20-5.
J1850 states that each message has a maximum length of 101 PWM bit
times or 12 VPW bytes, excluding SOF, EOD, NB, and EOF, with each
byte transmitted MSB first.
All VPW symbol lengths in the following descriptions are typical values
at a 10.4 kbps bit rate.
IDLE
SOF
DATA
PRIORITY
(DATA0)
MESSAGE ID
(DATA1)
DATA_N
E
OPTIONAL
CRC
ON
DB
IFR
I
F
EOF S IDLE
Figure 20-5. J1850 Bus Message Format (VPW)
SOF — Start-of-Frame Symbol
All messages transmitted onto the J1850 bus must begin with a
long-active 200-µs period SOF symbol. This indicates the start of a
new message transmission. The SOF symbol is not used in the CRC
calculation.
Data — In-Message Data Bytes
The data bytes contained in the message include the message
priority/type, message ID byte (typically the physical address of the
responder), and any actual data being transmitted to the receiving
node. The message format used by the BDLC is similar to the 3-byte
consolidated header message format outlined by the SAE J1850
document. See SAE J1850 — Class B Data Communications
Network Interface for more information about 1- and 3-byte headers.
Messages transmitted by the BDLC onto the J1850 bus must contain
at least one data byte and, therefore, can be as short as one data byte
and one CRC byte. Each data byte in the message is eight bits in
length and is transmitted MSB to LSB.
Advance Information
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Byte Data Link Controller-Digital (BDLC-D)
MC68HC08AS32 — Rev. 3.0
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