HC705V8GRSSLASHD datasheet(127/172 Pages) NXP

127 / 172 page

SECTION 15: MESSAGE DATA LINK CONTROLLER

Page 116

MC68HC705V8 Specification Rev. 2.1

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

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 VBATT.

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

transmits

but

receives invalid bits (noise).

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