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SECTION 15: MESSAGE DATA LINK CONTROLLER
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MOTOROLA
Page 111
including the CRC byte. Any messages received with more than the maximum number of
bytes will be discarded by the MDLC.
15.4.3.5.7
Invalid Active Level
If the MDLC transmits an active symbol but senses that the bus remains active longer than
163 us, then the MDLC will stop transmitting. The MDLC will treat this invalid active level
just like a received Break symbol. The MDLC will try to transmit the message again after
an idle bus is detected.
15.4.3.5.8
BREAK - Break
Any MDLC transmitting at the time a BREAK is detected will treat the BREAK as if a loss
of arbitration had occurred, and halt transmission. The MDLC will then retry to transmit the
message.
If while receiving a message the MDLC detects a BREAK symbol, it will treat the BREAK
as a reception error and clear the current Rx Buffer pointer.
Table 15-3: MDLC J1850 Bus Error Summary
Error Condition
MDLC Function
Bus short to V
BATT
.
The MDLC will not transmit until the bus is idle.
Bus short to Gnd.
The MDLC will try only once to send the message.
No interrupt will be generated.
MDLC
receives invalid bits (noise).
transmits
but
The MDLC will abort transmission immediately. No
interrupt will be generated.
MDLC receives invalid bit.
The MDLC will reset the Rx Buffer pointer and wait
for the next valid SOF. No interrupt will be generated.
MDLC receives message
framing error.
The MDLC will reset the Rx Buffer pointer and wait
for the next valid SOF. No interrupt will be generated.
MDLC receives under length
or over length message.
The MDLC will reset the Rx Buffer pointer and wait
for the next valid SOF. No interrupt will be generated.
MDLC receives invalid CRC
The MDLC will reset the Rx Buffer pointer and wait
for the next valid SOF. No interrupt will be generated.
MDLC
symbol
receives
BREAK
The MDLC will reset the Rx Buffer pointer and wait
for the next valid SOF. No interrupt will be generated.
MDLC sends an EOD but
receives an active symbol.
The MDLC will reset the Rx Buffer pointer and try to
resend that message after an idle bus.
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