MC68HC08AS32A Datasheet, PDF (92/296 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Byte Data Link Controller-Digital (BDLC-D)
NOTE:
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.
If the programmer attempts to set the TMIFR1 bit immediately after the EOD
symbol has been received from the bus, the TMIFR1 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 any byte of a
multiple byte IFR, the BDLC will go to the loss of arbitration state, set the
appropriate flag, and cease transmission.
If the BDLC loses arbitration during the IFR, the TMIFR1 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 will be sent out.
The extra logic 1s are an enhancement to the J1850 protocol which forces a byte
boundary condition fault. This is helpful in preventing noise from going onto the
J1850 bus from a corrupted message.
TMIFR0 — Transmit Multiple Byte IFR without CRC (Type 3) Bit
The TMIFR0 bit is used to request the BDLC to transmit the byte in the BDLC
data register (BDR) as the first byte of a multiple byte IFR without CRC.
Response IFR bytes are still subject to J1850 message length maximums (see
4.4.2 J1850 Frame Format and Figure 4-20).
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, the last IFR byte to be
transmitted will be the last byte which was written into the BDR register.
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 4.6.4 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
Data Sheet
92
Byte Data Link Controller-Digital (BDLC-D)
For More Information On This Product,
Go to: www.freescale.com
MC68HC08AS32A — Rev. 1
MOTOROLA