MC68HC08AS20 Datasheet, PDF (358/386 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

0 = The TMIFR0 bit will be cleared automatically, once the BDLC
has successfully transmitted the EOD symbol, by the detection
of an error on the multiplex bus or by a transmitter underrun
caused when the programmer does not write another byte to
the BDR after the TDRE interrupt.
If the TMIFR0 bit is set, the BDLC will attempt to transmit the
normalization symbol followed by the byte in the BDR. After the byte
in the BDR has been loaded into the transmit shift register, a TDRE
interrupt (see 20.7.4 BDLC State Vector Register) will occur similar
to the main message transmit sequence. The programmer should
then load the next byte of the IFR into the BDR for transmission.
When the last byte of the IFR has been loaded into the BDR, the
programmer should set the TEOD bit in the BCR2. This will instruct
the BDLC to transmit an EOD symbol once the byte in the BDR is
transmitted, indicating the end of the IFR portion of the message
frame. The BDLC will not append a CRC when the TMIFR0 is set.
If the programmer attempts to set the TMIFR0 bit after the EOD
symbol has been received from the bus, the TMIFR0 bit will remain in
the reset state, and no attempt will be made to transmit an IFR byte.
If a loss of arbitration occurs when the BDLC is transmitting, the
TMIFR0 bit will be cleared, and no attempt will be made to retransmit
the byte in the BDR. If loss of arbitration occurs in the last two bits of
the IFR byte, two additional 1 bits (active short bits) will be sent out.
NOTE:
The extra logic 1s are an enhancement to the J1850 protocol which
forces a byte boundary condition fault. This is helpful in preventing noise
on to the J1850 bus from a corrupted message.
20.7.4 BDLC State Vector Register
This register is provided to substantially decrease the CPU overhead
associated with servicing interrupts while under operation of a multiplex
protocol. It provides an index offset that is directly related to the BDLC’s
current state, which can be used with a user-supplied jump table to
Advance Information
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MC68HC08AS20 —Rev. 4.1
Freescale Semiconductor