Freescale Semiconductor MPC5200B - Manual (Page 689)

MPC5200B Users Guide, Rev. 1
20-10 Freescale Semiconductor
Memory Map and Registers
The BDLC supports the In-frame Response (IFR) feature of J1850 by setting these bits correctly. The four types of J1850 IFR are shown
in
Figure 20-3 . The purpose of the in-frame response modes is to allow single or multiple nodes to acknowledge receipt of the data by
responding to a received message after they have seen the EOD symbol. 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.
Figure 20-3. Types of In-Frame Response
TSIFR
—
Transmit Single Byte IFR with no CRC (Type 1 or 2)
This bit is used to request the BDLC to transmit the byte in the BDLC Data Register as a single byte IFR with no CRC. Typically, the byte
transmitted is a unique identifier or address of the transmitting (responding) node.
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
module will attempt to transmit the appropriate normalization bit followed by the byte in the BDLC Data Register.
0 = The TSIFR bit will be automatically cleared once the EOD following one or more IFR bytes has been received or an error is
detected on the bus.
The user must set the TSIFR bit before the EOF following the main part of the message frame is received, or no IFR transmit attempts will
be made for the current message. If another node transmits an IFR to this message, the user must set the TSIFR bit before the normalization
bit is received or no IFR transmit attempts will be made for the message. If another node does transmit a successful IFR or a reception error
occurs, the TSIFR bit will be cleared. If not, the IFR will be transmitted after the EOD of the next received message.
If a loss of arbitration occurs when the BDLC module attempts transmission, after the IFR byte winning arbitration completes transmission,
the BDLC module will again attempt to transmit the byte in the BDLC Data Register (with no normalization bit). The BDLC module will
continue transmission attempts until an error is detected on the bus, or TEOD is set by the CPU, or the BDLC transmission is successful.
NOTE
Setting the TEOD bit before transmission of the IFR byte will direct the BDLC to make only one
attempt at transmitting the byte.
If loss of arbitration occurs in the last bit of the IFR byte, two additional ‘1’ bits will not be sent out because the BDLC will attempt to
retransmit the byte in the transmit shift register after the IFR byte winning arbitration completes transmission.
TMIFR1
—
Transmit Multiple Byte IFR with CRC (Type 3)
This bit requests the BDLC module to transmit the byte in the BDLC Data Register (BDLC Data Register) as the first byte of a multiple byte
IFR with CRC or as a single byte IFR with CRC.Response IFR bytes are still subject to J1850 message length maximums.
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
module will attempt to transmit the appropriate normalization bit followed by IFR bytes.The programmer should set TEOD after
the last IFR byte has been written into BDLC Data Register. After TEOD has been set and the last IFR byte has been transmitted,
the CRC byte is transmitted.
0 = The TMIFR1 bit will be automatically cleared once the BDLC module has successfully transmitted the CRC byte and EOD
symbol, by the detection of an error on the multiplex bus, a transmitter underrun, or loss of arbitration.
SOF
Header Data Field CRC
EOD
Type 0 - No IFR
Header Data Field CRC
EOD
Type 3 - Multiple Bytes From a Single Responder (with or without CRC)
Header Data Field CRC
EOD
Type 1 - Single Byte From a Single Responder (without CRC)
Header Data Field CRC
EOD
Type 2 - Single Byte From Multiple Responders (without CRC)
ID1 ID n
IFR Data Field CRC
NB
NB
NB
ID
SOF
SOF
SOF
EOF
EOD EOF
EOD EOF
EOD EOF