MC908AS60ACFU Datasheet, PDF (359/414 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

BDLC CPU Interface
TSIFR — Transmit Single Byte IFR with No CRC (Type 1 or 2) Bit
The TSIFR bit is used to request the BDLC to transmit the byte in the BDLC data register (BDR, $003F)
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 27-18.
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 will attempt to transmit the appropriate normalization bit followed
by the byte in the BDR.
0 = The TSIFR bit will be 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 will remain in the reset state and no attempt will be 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 will again attempt to transmit the BDR (with no
normalization bit). The BDLC will continue transmission attempts until an error is detected on the bus, or
TEOD is set, or the BDLC transmission is successful.
If loss or arbitration occurs in the last two bits 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 IRF byte
winning arbitration completes transmission.
TMIFR1 — Transmit Multiple Byte IFR with CRC (Type 3) Bit
The TMIFR1 bit requests the BDLC to transmit the byte in the BDLC data register (BDR) 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 (see J1850 Frame Format and Figure 27-18).
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 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
the BDR 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 cleared automatically – once the BDLC has successfully transmitted the
CRC byte and 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 TMIFR1 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 27.6.4 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
BDLC control register 2 (BCR2). This will instruct the BDLC to transmit a CRC byte once the byte in
the BDR is transmitted and then transmit an EOD symbol, indicating the end of the IFR portion of the
message frame.
However, if the programmer wishes to transmit a single byte followed by a CRC byte, the programmer
should load the byte into the BDR before the EOD symbol has been received, and then set the TMIFR1
bit. Once the TDRE interrupt occurs, the programmer should then set the TEOD bit in the BCR2. This
will result in the byte in the BDR being the only byte transmitted before the IFR CRC byte, and no TDRE
interrupt will be generated.
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
Freescale Semiconductor
359