MAC7200 datasheet(733/976 Pages) FREESCALE

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Functional Description

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

655

31.10.4.4 Idle Characters

An idle character contains all logic 1s and has no start, stop, or parity bit. Idle character length depends on

the M bit in SCI control register 1 (SCICR1). The preamble is a synchronizing idle character that begins

the first transmission initiated after writing the TE bit from 0 to 1.

If the TE bit is cleared during a transmission, the Tx output signal becomes idle after completion of the

transmission in progress. Clearing and then setting the TE bit during a transmission queues an idle

character to be sent after the frame currently being transmitted.

NOTE

When queueing an idle character, return the TE bit to logic 1 before the stop

bit of the current frame shifts out through the Tx output signal. Setting TE

after the stop bit appears on Tx output signal causes data previously written

to the SCI data register to be lost. Toggle the TE bit for a queued idle

character while the TDRE flag is set and immediately before writing the

next byte to the SCI data register.

31.10.4.5 Standard Bit Error Detection

Standard Bit Error Detection implements the Bit Error Detection algorithm that is normally used by a

software implementation of the LIN protocol. During a transmit frame or while the header of a RX frame

is sent, it reads the received byte and compares it to the one which was sent out. If there are any mismatches

between the 8 transmitted databits and the 8 received databits, the BERR flag will be set.

31.10.4.6 Fast Bit Error Detection in LIN mode

Fast Bit Error Detection has been designed to allow flagging of LIN bit errors while they occur, rather than

flagging them after a byte transmission has completed (see Figure 31-24).

Figure 31-24. Fast Bit Error Detection on a LIN Bus

TXD Pin

RXD Pin

LIN Physical Interface

Synchronizer Stage

Bus Clock

Receive Shift

Transmit Shift

LIN Bus

Compare

Sample Point

Bit Error

MAC7200 Datasheet(PDF) 733 Page - Freescale Semiconductor, Inc