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: 42/170页
文件大小: 589K
代理商: MC68HC05V7FN
MOTOROLA
SECTION 15: MESSAGE DATA LINK CONTROLLER
Page 122
MC68HC05V7 Specification Rev. 1.0
During arbitration, or even throughout the message being transmitted, when an opposite
bit is detected, transmission is immediately stopped unless it occurs on the 8th bit of a byte.
In this case the MDLC will automatically append up to two extra 1 bits and then stop
transmitting. These two extra bits will be arbitrated normally and thus will not interfere with
another message. The second 1 bit will not be sent if the first loses arbitration. If the MDLC
has lost arbitration to another valid message then the two extra ones will not corrupt the
current message. However, if the MDLC has lost arbitration due to noise on the bus, then
the two extra ones will ensure that the current message will be detected and ignored as a
noise-corrupted message.
Since a "0" dominates a "1", the message with the lowest value will have the highest
priority, and will always win arbitration, i.e. a message with priority 000 will win arbitration
over a message with priority 001. This method of arbitration will work no matter how many
bits of priority encoding are contained in the message.
If the MDLC loses arbitration during the transmission of a message, it will attempt to
retransmit as soon as a valid EOF is detected on the J1850 bus. The MDLC will attempt to
retransmit the message indefinitely, as long as messages with higher priorities continue to
win arbitration.
The only way to stop transmission retry due to loss of arbitration is to abort the transmission
by setting the Tx Abort (TXAB) bit in the MDLC Control register. This will reset the internal
Tx Buffer pointer and halt transmission.
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