参数资料
型号: MC68HC05V7FN
厂商: MOTOROLA INC
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 2.1 MHz, MICROCONTROLLER, PQCC68
封装: PLASTIC, LCC-68
文件页数: 29/170页
文件大小: 589K
代理商: MC68HC05V7FN
MOTOROLA
SECTION 15: MESSAGE DATA LINK CONTROLLER
Page 110
MC68HC05V7 Specification Rev. 1.0
If the MDLC is transmitting a message and the message received contains invalid bits, or
framing symbols on non-byte boundaries, this constitutes a transmission error. When a
transmission error is detected, the MDLC will immediately cease transmitting.
If the MDLC is receiving a message and it detects an error during the message, the
message is discarded. No message with an error contained in it is passed to the CPU and
no error status information is available.
15.4.3.5.1
CRC Error
A CRC error is detected when the data bytes and CRC byte of a received message are
processed, and the CRC calculation result is not equal to $C4. The CRC code should
detect any single and 2 bit errors, as well as all 8 bit burst errors, and almost all other types
of errors.
15.4.3.5.2
Bit Format Error
A Bit Format error is detected when an abnormal (invalid) bit is detected in a message
being received from the J1850 bus. However, if the MDLC is transmitting when this
happens, it will be treated as a loss of arbitration rather than a transmitter error and the
automatic retry mechanism will apply.
15.4.3.5.3
Message Format Error
A Message Format error is detected if an EOD or EOF symbol is detected on a non-byte
boundary from the J1850 bus.
15.4.3.5.4
Bus Fault
If a bus fault occurs, the response of the MDLC will depend upon the type of bus fault.
If the bus is shorted to Vbatt, the MDLC will wait for the bus to fall to a passive state before
it will attempt to transmit a message. As long as the short remains, the MDLC will never
attempt to transmit a message onto the J1850 bus.
If the bus is shorted to ground, the MDLC will see an idle bus, begin to transmit the
message, and then detect a transmission error, since the short to ground would not allow
the bus to be driven to the dominant state. The MDLC will abort that transmission and wait
for the next CPU command to transmit.
In any case, if the bus fault is temporary, as soon as the fault is cleared, the MDLC will
resume normal operation. If the bus fault is permanent, it may result in permanent loss of
communication on the J1850 bus.
15.4.3.5.5
Message Under Length Error
Any message received by the MDLC must be at least two bytes long. Since the MDLC does
not have message filtering, these two bytes could just be one data byte and a CRC byte.
Any messages received with less than the minimum number of bytes will be discarded by
the MDLC.
15.4.3.5.6
Message Over Length Error
A Message Over Length error is detected when a message being received exceeds the
maximum length allowed for a message on the J1850 bus. If the Receive Block mode
(RXBM) bit is not set, the maximum received length from SOF to the EOD is 12 bytes
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