MC68HC908AT32 Datasheet, PDF (345/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

BDLC Protocol Handler
Symbol Error
A symbol error is detected when an abnormal (invalid) symbol is detected in a message being received
from the J1850 bus. The invalid symbol is set when a symbol error is detected. (See 28.6.4 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 symbol invalid, or the out-of-range flag, is set when a framing error is detected.
(See 28.6.4 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 (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 28.6.4 BDLC State Vector Register.)
BREAK — Break
If a BREAK symbol is received while the BDLC is transmitting or receiving, an invalid symbol (in BSVR)
interrupt will be generated. Reading the BSVR (see 28.6.4 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 only can receive a BREAK symbol from the J1850 bus.
MC68HC908AT32 Data Sheet, Rev. 3.1
Freescale Semiconductor
345