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MC908AZ60ACFUER Datasheet, PDF (352/414 Pages) Freescale Semiconductor, Inc – To provide the most up-to-date information, the revision of our documents on the World Wide Web will be the most current. Your printed copy may be an earlier revision. To verify you have the latest information available, refer to:
Byte Data Link Controller (BDLC)
CRC Error
A cyclical redundancy check (CRC) error is detected when the data bytes and CRC byte of a received
message are processed and the CRC calculation result is not equal to $C4. The CRC code will detect
any single and 2-bit errors, as well as all 8-bit burst errors and almost all other types of errors. The
CRC error flag ($18 in BSVR) is set when a CRC error is detected. (See 27.6.4 BDLC State Vector
Register.)
Symbol Error
A symbol error is detected when an abnormal (invalid) symbol is detected in a message being received
from the J1850 bus. However, if the BDLC is transmitting when this happens, it will be treated as a loss
of arbitration ($14 in BSVR) rather than a transmitter error. The ($1C) symbol invalid or the
out-of-range flag is set when a symbol error is detected. Therefore, ($1C) symbol invalid flag is stacked
behind the ($14) LOA flag during a transmission error process. (See 27.6.4 BDLC State Vector
Register.)
Framing Error
A framing error is detected if an EOD or EOF symbol is detected on a non-byte boundary from the
J1850 bus. A framing error also is detected if the BDLC is transmitting the EOD and instead receives
an active symbol. The ($1C) symbol invalid or the out-of-range flag is set when a framing error is
detected. (See 27.6.4 BDLC State Vector Register.)
Bus Fault
If a bus fault occurs, the response of the BDLC will depend upon the type of bus fault.
If the bus is shorted to battery, the BDLC will wait for the bus to fall to a passive state before it will
attempt to transmit a message. As long as the short remains, the BDLC will never attempt to transmit
a message onto the J1850 bus.
If the bus is shorted to ground, the BDLC will see an idle bus, begin to transmit the message, and then
detect a transmission error ($1C in BSVR), since the short to ground would not allow the bus to be
driven to the active (dominant) SOF state. The BDLC will abort that transmission and wait for the next
CPU command to transmit.
In any case, if the bus fault is temporary, as soon as the fault is cleared, the BDLC will resume normal
operation. If the bus fault is permanent, it may result in permanent loss of communication on the J1850
bus. (See BDLC State Vector Register.)
BREAK — Break
If a BREAK symbol is received while the BDLC is transmitting or receiving, an invalid symbol ($1C in
BSVR) interrupt will be generated. Reading the BSVR register (see 27.6.4 BDLC State Vector
Register.) will clear this interrupt condition. The BDLC will wait for the bus to idle, then wait for a
start-of-frame (SOF) symbol.
The BDLC cannot transmit a BREAK symbol. It can only receive a BREAK symbol from the J1850 bus.
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
352
Freescale Semiconductor