
Byte Data Link Communications (BDLC)
BDLC Registers
MC68HC912B32 MC68HC12BE32 — Rev. 3.0
Advance Information
MOTOROLA
Byte Data Link Communications (BDLC)
339
The purpose of the in-frame response modes is to allow multiple
nodes to acknowledge receipt of the data by responding with their
personal ID or physical address in a concatenated manner after they
have seen the EOD symbol. If transmission arbitration is lost by a
node while sending its response, it continues to transmit its
ID/address until observing its unique byte in the response stream. For
VPW modulation, the first bit of the IFR is always passive; therefore,
an active normalization bit must be generated by the responder and
sent prior to its ID/address byte. When there are multiple responders
on the J1850 bus, only one normalization bit is sent which assists all
other transmitting nodes to sync their responses.
TSIFR — Transmit Single Byte IFR with No CRC Bit (Type 1 and Type 2)
The TSIFR bit is used to request the BDLC to transmit the byte in the
BDLC data register (BDR) as a single byte IFR with no CRC.
Typically, the byte transmitted is a unique identifier or address of the
transmitting (responding) node. See
Figure 15-14
.
1 = If this bit is set prior to a valid EOD being received with no CRC
error, once the EOD symbol has been received the BDLC
attempts to transmit the appropriate normalization bit followed
by the byte in the BDR.
0 = TSIFR bit is cleared automatically, once the BDLC
has successfully transmitted the byte in the BDR onto the
bus, or TEOD is set, or an error is detected on the bus.
If the programmer attempts to set the TSIFR bit immediately after the
EOD symbol has been received from the bus, the TSIFR bit remains
in the reset state and no attempt is made to transmit the IFR byte.
If a loss of arbitration occurs when the BDLC attempts to transmit and
after the IFR byte winning arbitration completes transmission, the
BDLC again attempts to transmit the BDR (with no normalization bit).
The BDLC continues transmission attempts until an error is detected
on the bus, or TEOD is set, or the BDLC transmission is successful.
If loss of arbitration occurs in the last bit of the IFR byte, two additional
1 bits are not sent out because the BDLC attempts to retransmit the
byte in the transmit shift register after the IRF byte winning arbitration
completes transmission.