HC05V7GRSSLASHD datasheet(136/170 Pages) NXP

136 / 170 page

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.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

HC05V7GRS/D Scheda tecnica(PDF) 136 Page - NXP Semiconductors