MAC7200 datasheet(591/976 Pages) FREESCALE

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The Generic FlexCAN2 Module

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

513

Table 28-7. Message Buffer Code for Rx buffers

Rx Code

BEFORE

Rx New Frame

Description

Rx Code AFTER

Rx New Frame

Comment

0000

INACTIVE: MB is not active.

–

MB does not participate in the matching process.

0100

EMPTY: MB is active and empty.

0010

MB participates in the matching process. When a

frame is received successfully, the code is

automatically updated to FULL.

0010

FULL: MB is full.

0010

The act of reading the C/S word followed by

unlocking the MB does not make the code return to

EMPTY. It remains FULL. If a new frame is written

to the MB after the C/S word was read and the MB

was unlocked, the code still remains FULL.

0110

If the MB is FULL and a new frame is overwritten to

this MB before the CPU had time to read it, the code

is automatically updated to OVERRUN. Refer to

Section 28.2.7.5, “Matching Process,” for details

about overrun behavior.

0110

OVERRUN: a frame was

overwritten into a full buffer.

0010

If the code indicates OVERRUN but the CPU reads

the C/S word and then unlocks the MB, when a new

frame is written to the MB the code returns to FULL.

0110

If the code already indicates OVERRUN, and yet

another new frame must be written, the MB will be

overwritten again, and the code will remain

OVERRUN. Refer to Section 28.2.7.5, “Matching

Process,” for details about overrun behavior.

0XY11

1. Note that for Tx MBs (see Table 28-8), the BUSY bit should be ignored upon read.

BUSY: Flexcan is updating the

contents of the MB. The CPU must

not access the MB.

0010

An EMPTY buffer was written with a new frame (XY

was 01).

0110

A FULL/OVERRUN buffer was overwritten (XY was

11).

Table 28-8. Message Buffer Code for Tx buffers

RTR

Initial Tx code

Code after

successful

transmission

Description

1000

–

INACTIVE: MB does not participate in the arbitration process.

1100

1000

Transmit data frame unconditionally once. After transmission, the MB

automatically returns to the INACTIVE state.

1100

0100

Transmit remote frame unconditionally once. After transmission, the MB

automatically becomes an Rx MB with the same ID.

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