Tx Buffer Element

The Tx Buffers section can be configured to hold dedicated Tx Buffers as well as a Tx FIFO / Tx Queue. In case that the Tx Buffers section is shared by dedicated Tx buffers and a Tx FIFO / Tx Queue, the dedicated Tx Buffers start at the beginning of the Tx Buffers section followed by the buffers assigned to the Tx FIFO or Tx Queue. The Tx Handler distinguishes between dedicated Tx Buffers and Tx FIFO / Tx Queue by evaluating the Tx Buffer configuration TXBC.TFQS and TXBC.NDTB. The element size can be configured for storage of CAN FD messages with up to 64 bytes data field via register TXESC.

Table 1. Tx Buffer Element
	31				24	23					16	15	8	7	0
T0	ESI	XTD	RTR	ID[28:0]
T1	MM[7:0]					EFC	reserved	FDF	BRS	DLC[3:0]		reserved
T2	DB3[7:0]					DB2[7:0]						DB1[7:0]		DB0[7:0]
T3	DB7[7:0]					DB6[7:0]						DB5[7:0]		DB4[7:0]
...	...					...						...		...
Tn	DBm[7:0]					DBm-1[7:0]						DBm-2[7:0]		DBm-3[7:0]

• T0 Bit 30 ESI: Error State Indicator

T0 Bit 31 ESI: Error State Indicator

0: ESI bit in CAN FD format depends only on error passive flag

1: ESI bit in CAN FD format transmitted recessive

Note: The ESI bit of the transmit buffer is or’ed with the error passive flag to decide the value of the ESI bit in the transmitted FD frame. As required by the CAN FD protocol specification, an error active node may optionally transmit the ESI bit recessive, but an error passive node will always transmit the ESI bit recessive. This feature can be used in gateway applications when a message from an error passive node is routed to another CAN network.

• T0 Bit 30 XTD: Extended Identifier

0: 11-bit standard identifier.

1: 29-bit extended identifier.

• T0 Bit 29 RTR: Remote Transmission Request

0: Transmit data frame.

1: Transmit remote frame.

Note: When RTR = 1, the MCAN transmits a remote frame according to ISO11898-1, even if MCAN_CCCR.FDOE enables the transmission in CAN FD format.

• T0 Bits 28:0 ID[28:0]: Identifier

Standard or extended identifier depending on bit XTD. A standard identifier has to be written to ID[28:18].

• T1 Bits 31:24 MM[7:0]: Message Marker

Written by processor during Tx Buffer configuration. Copied into Tx Event FIFO element for identification of Tx message status.

• T1 Bit 23 EFC: Event FIFO Control

0: Do not store Tx events.

1: Store Tx events.

• T1 Bit 21 FDF: FD Format

0: Frame transmitted in Classic CAN format

1: Frame transmitted in CAN FD format

• T1 Bit 20 BRS: Bit Rate Switching

0: CAN FD frames transmitted without bit rate switching

1: CAN FD frames transmitted with bit rate switching

Note:

Bits ESI, FDF, and BRS are only evaluated when CAN FD operation is enabled (MCAN_CCCR.FDOE = 1). Bit BRS is only evaluated when in addition MCAN_CCCR.BRSE = 1.

• T1 Bits 19:16 DLC[3:0]: Data Length Code

0-8: CAN + CAN FD: transmit frame has 0-8 data bytes.

9-15: CAN: transmit frame has 8 data bytes.

9-15: CAN FD: transmit frame has 12/16/20/24/32/48/64 data bytes.

• T2 Bits 31:24 DB3[7:0]: Data Byte 3

• T2 Bits 23:16 DB2[7:0]: Data Byte 2

• T2 Bits 15:8 DB1[7:0]: Data Byte 1

• T2 Bits 7:0 DB0[7:0]: Data Byte 0

• T3 Bits 31:24 DB7[7:0]: Data Byte 7

• T3 Bits 23:16 DB6[7:0]: Data Byte 6

• T3 Bits 15:8 DB5[7:0]: Data Byte 5

• T3 Bits 7:0 DB4[7:0]: Data Byte 4

... ... ...

• Tn Bits 31:24 DBm[7:0]: Data Byte m

• Tn Bits 23:16 DBm-1[7:0]: Data Byte m-1

• Tn Bits 15:8 DBm-2[7:0]: Data Byte m-2

• Tn Bits 7:0 DBm-3[7:0]: Data Byte m-3

Note: Depending on the configuration of the element size (MCAN_TXESC), between two and sixteen 32-bit words (Tn = 3 ..17) are used for storage of a CAN message’s data field.