Datasheet

Byte Data Link Controller (BDLC)
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
358 Freescale Semiconductor
TSIFR, TMIFR1, and TMIFR0 — Transmit In-Frame Response Control Bits
These three bits control the type of in-frame response being sent. The programmer should not set
more than one of these control bits to a 1 at any given time. However, if more than one of these three
control bits are set to 1, the priority encoding logic will force these register bits to a known value as
shown in Table 27-4. For example, if 011 is written to TSIFR, TMIFR1, and TMIFR0, then internally
they will be encoded as 010. However, when these bits are read back, they will read 011.
The BDLC supports the in-frame response (IFR) feature of J1850 by setting these bits correctly. The
four types of J1850 IFR are shown below. 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, because the first bit of the IFR is always
passive, a normalization bit (active) 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 up their response.
Figure 27-18. Types of In-Frame Response (IFR)
Table 27-4. BDLC Transmit In-Frame Response
Control Bit Priority Encoding
Write/Read
TSIFR
Write/Read
TMIFR1
Write/Read
TMIFR0
Actual
TSIFR
Actual
TMIFR1
Actual
TMIFR0
000000
1XX100
01X010
001001
SOF
HEADER DATA FIELD CRC
EOD
TYPE 0 — NO IFR
HEADER
DATA FIELD CRC
EOD
TYPE 3 — MULTIPLE BYTES TRANSMITTED FROM A SINGLE RESPONDER
HEADER DATA FIELD CRC
EOD
TYPE 1 — SINGLE BYTE TRANSMITTED FROM A SINGLE RESPONDER
HEADER DATA FIELD
CRC
EOD
TYPE 2 — SINGLE BYTE TRANSMITTED FROM MULTIPLE RESPONDERS
ID1
ID N
IFR DATA FIELD
CRC
NB
NB
NB
ID
SOF
SOF
SOF
EOF
EOD EOF
EOD EOF
EOD EOF
(OPTIONAL)
NB = Normalization Bit
ID = Identifier (usually the physical address of the responder(s))
HEADER = Specifies one of three frame lengths