HC05V7GRSSLASHD datasheet(111/170 Pages) NXP

111 / 170 page

SECTION 15: MESSAGE DATA LINK CONTROLLER

Page 97

MC68HC05V7 Specification Rev. 1.0

If this command is recognized by the MDLC while one of the first seven bits of a byte is

being transmitted (non-byte boundary) then the transmission of the bit will be completed

and no further bits will be sent.

If this command is recognized while the last bit of a byte is being transmitted (byte

boundary) then the transmission of the bit will first be completed. In order to avoid receiving

nodes from interpreting the aborted transmission at a byte boundary as being the end of a

normal message, the MDLC will then send two extra logic one bits.

This guarantees that no aborted message will be an integral number of bytes in length and

cannot be mistaken for a valid transmission.

Arbitration will be performed on any extra bits sent, allowing any other nodes which are also

transmitting to continue. Should the MDLC lose arbitration during the first extra logic one

sent, the second extra logic one will not be sent and no further attempts to send the

message will be made.

If this command is recognized after a write to the MDLC Transmit Control Register (MTCR),

thus initiating a transmission, but before the message has begun to be sent on the J1850

bus, then no attempt to transmit that message will be made until a subsequent write to the

MTCR is made.

If this command is recognized between automatic transmission retry attempts, such as

those following a loss of arbitration, all further attempts to resend the message will be

suppressed.

This bit is automatically cleared after the abort takes place or after it is determined that the

MDLC was not transmitting anyway. Refer to Table 15-1:

MDLC Transmit Abort

Function Summary for a summary of the operation of the TXAB bit.

The programmer must never write to the MTCR register while the TXAB bit is set, as this

may have unpredictable results.

Table 15-1:

MDLC Transmit Abort Function Summary

Transmit Abort Command

MDLC Action

Command recognized on

non-byte boundary

MDLC will terminate transmission immediately

Command recognized on

byte boundary

MDLC will transmit up to two extra ones

Command recognized

before the message has

started on the J1850 bus

MDLC will not transmit the message

Command recognized

during retry

MDLC will not retry to transmit the message

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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