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Chapter 16
CAN Controller
User’s Manual U16504EE1V1UD00
16.8 Transmit Buffer Structure
The DCAN has two independent transmit buffers. The two buffers have a 16 byte data structure for
standard and extended frames with the ability to send up to 8 data bytes per message. The structure of
the transmit buffer is similar to the structure of the receive buffers. The CPU can use addresses that are
specified as “unused” in the transmit buffer layout. As well the CPU may use unused ID addresses,
unused data addresses
Note
, and an unused transmit buffer of the DCAN for its own purposes. The con-
trol bits, the identification and the message data have to be stored in the message RAM area.
The transmission control is done by the TCR register. A transmission priority selection allows the cus-
tomer to realize an application specific priority selection. After the priority selection the transmission
can be started by setting the TXRQn bit (n = 0, 1).
In the case that both transmit buffers are used, the transmit priorities can be set. For this purpose the
DCAN has the TXP bit in the TCR register. The application software has to set this priority before the
transmission is started.
The two transmit buffers supply two independent interrupt lines for an interrupt controller.
Note:
Message objects that need less than 8 data byte (DLC < 8) may use the remaining bytes
(8 - DLC) for application purposes.
16.9 Transmit Message Format
Note:
This address is a relative offset to the starting address of the transmit buffer.
Table 16-20:
Transmit Message Format
Name
Address
Note
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
TCON
n0H
IDE
RTR
0
0
DLC3
DLC2
DLC1
DLC0
n1H
Unused
IDTX0
n2H
ID standard part
IDTX1
n3H
ID standard part
0
0
0
0
0
IDTX2
n4H
ID extended part
IDTX3
n5H
ID extended part
IDTX4
n6H
ID extended part
0
0
0
0
0
0
n7H
Unused
DATA0
n8H
Message data byte 0
DATA1
n9H
Message data byte 1
DATA2
nAH
Message data byte 2
DATA3
nBH
Message data byte 3
DATA4
nCH
Message data byte 4
DATA5
nDH
Message data byte 5
DATA6
nEH
Message data byte 6
DATA7
nFH
Message data byte 7