NXP Semiconductors KE1xF Series, Reference Manual, Page: 1439 / 1483

50.5.3 Receive process
To be able to receive CAN frames into a Mailbox, the CPU must prepare it for reception
by executing the following steps:
1. If the Mailbox is active (either Tx or Rx) inactivate the Mailbox (see Mailbox
inactivation ), preferably with a safe inactivation (see Transmission abort
mechanism ).
2. Write the ID word
3. Write the EMPTY code (0b0100) to the CODE field of the Control and Status word
to activate the Mailbox.
After the MB is activated, it will be able to receive frames that match the programmed
filter. At the end of a successful reception, the Mailbox is updated by the move-in process
(see
Move-in ) as follows:
1. The received Data field (8 bytes at most for Classical CAN message format) is
stored.
2. The received Identifier field is stored.
3. The value of the Free Running Timer at the time of the second bit of frame's
Identifier field is written into the Mailbox's Time Stamp field.
4. The received SRR, IDE, RTR and DLC fields are stored.
5. The CODE field in the Control and Status word is updated (see Table 50-5 and Table
50-6 in Section Message buffer structure ).
6. 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 recommended way for CPU servicing (read) the frame received in an Mailbox is
using the following procedure:
1. Read the Control and Status word of that Mailbox.
2. Check if the BUSY bit is deasserted, indicating that the Mailbox is locked. Repeat
step 1) while it is asserted. See Mailbox lock mechanism .
3. Read the contents of the Mailbox. Once Mailbox is locked now, its contents won't be
modified by FlexCAN Move-in processes. See Move-in .
4. Acknowledge the proper flag at IFLAG registers.
Chapter 50 CAN (FlexCAN)
Kinetis KE1xF Sub-Family Reference Manual, Rev. 4, 06/2019
NXP Semiconductors 1439