Transmit Process - NXP Semiconductors freescale KV4 Series Reference Manual

Table of Contents

Functional description

Before proceeding with the functional description, an important concept must be

explained. A Message Buffer is said to be "active" at a given time if it can participate in

both the Matching and Arbitration processes. An Rx MB with a 0b0000 code is inactive

43-106). Similarly, a Tx MB with a 0b1000 or 0b1001 code is also

inactive (refer to

43.5.1 Transmit process

To transmit a CAN frame, the CPU must prepare a Message Buffer for transmission by

executing the following procedure:

1. Check whether the respective interrupt bit is set and clear it.

2. If the MB is active (transmission pending), write the ABORT code (0b1001) to the

CODE field of the Control and Status word to request an abortion of the

transmission. Wait for the corresponding IFLAG bit to be asserted by polling the

CAN_IFLAG register or by the interrupt request if enabled by the respective IMASK

bit. Then read back the CODE field to check if the transmission was aborted or

transmitted (see

desired (CAN_MCR[AEN] bit is negated), just write the INACTIVE code (0b1000)

to the CODE field to inactivate the MB but then the pending frame may be

transmitted without notification (see

3. Write the ID word.

4. Write the data bytes.

5. Write the DLC, Control, and CODE fields of the Control and Status word to activate

When the MB is activated, it participates in the arbitration process and is eventually

transmitted according to its priority.

At the end of the successful transmission, the value of the Free Running Timer is written

into the Time Stamp field, the CODE field in the Control and Status word is updated, the

CRC Register is updated, a status flag is set in the Interrupt Flag Register and an interrupt

is generated if allowed by the corresponding Interrupt Mask Register bit. The new CODE

field after transmission depends on the code that was used to activate the MB (see

Table 43-107

Transmission abort

mechanism). If backwards compatibility is

Message buffer

KV4x Reference Manual, Rev. 2, 02/2015

inactivation).

Freescale Semiconductor, Inc.