MC68HC58 Motorola, MC68HC58 Datasheet - Page 69

• Manufacturer Part Number: MC68HC58
• Description: Data Link Controller
• Manufacturer: Motorola

5.1.1.5 Terminate Auto Retry
5.1.1.6 Send IFR on EOD without CRC
MC68HC58
TECHNICAL DATA
If a frame is in progress on the J1850 bus (no EOD has been detected) when this com-
mand is latched, the DLC sends the IFR only if no receiver errors are detected. When
receiver errors are detected, the IFR is not transmitted, and is lost. If this occurs, the
DLC status byte indicates that the TxFIFO buffer is empty, and the DLC does not ter-
minate automatic retry.
If the DLC is transmitting when this command is latched, a timing error or an incom-
plete byte error will occur. The TxFIFO buffer is flushed, and both the frame and the
IFR are lost.
When additional IFR bytes are required, they must be placed in the TxFIFO buffer rap-
idly enough to prevent underrun. The second IFR byte must be loaded before the fall-
ing edge of the Normalization bit, and subsequent bytes must be loaded within 500 s
of each other. If a TxFIFO underrun occurs, it is flagged as an error, and the CRC byte
is complemented and appended to the IFR being transmitted.
The “terminate auto retry” command disables automatic retry. A DLC will normally at-
tempt to retransmit a frame that loses arbitration unless it is sending an IFR or a block
mode transmission.
If this command is latched while a transmission is in progress, the DLC attempts to
complete the frame. After the frame is successfully transmitted, or after it loses arbi-
tration, automatic retry terminates and the TxFIFO buffer is flushed.
If this command is latched while a complete frame that has lost arbitration is in the
buffer awaiting retransmission, the DLC attempts to retransmit the frame once more.
After the frame is sent, automatic retry terminates and the TxFIFO buffer is flushed.
If this command is latched while a complete frame that has not been transmitted is in
the buffer awaiting transmission, the DLC attempts to send the frame once, then au-
tomatic retry terminates and the TxFIFO buffer is flushed.
The “send IFR on EOD without CRC” command causes a DLC to clear the transmitter
and TxFIFO buffer, terminate automatic frame retransmission, and originate an IFR
with no CRC. This command must accompany a data byte, and the command byte
BTAD field must indicate either “load as first byte of transmit data” or “load as first and
last byte of transmit data”. The subsequent bytes in the same IFR must not be accom-
panied by this command.
If this command is latched while the J1850 bus is idle, or between EOD and EOF, the
IFR is not transmitted, and is lost. When this occurs, the DLC status byte indicates that
the TxFIFO buffer is empty, and the DLC does not terminate automatic retry.
CONTROL AND STATUS CODES
MOTOROLA
5-3