Structure Of A Message Object; Message Object Field Descriptions - Texas Instruments Concerto F28M36 Series Technical Reference Manual

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During normal operation, accesses to the Message RAM are performed via the Interface Register sets,
and the CPU cannot directly access the Message RAM.
The Interface register sets IF1 and IF2, provide indirect read/write access from the CPU to the Message
RAM. The IF1 and IF2 register sets can buffer control and user data to be transferred to and from the
message objects.
The third Interface register set IF3 can be configured to automatically receive control and user data from
the Message RAM when a message object has been updated after reception of a CAN message. The
CPU does not need to initiate the transfer from Message RAM to the IF3 register set.
The message handler avoids potential conflicts between concurrent accesses to Message RAM and CAN
frame reception/transmission.
The message RAM can only be accessed in debug mode. The message RAM base address is 0x2000
above the base address of the CAN peripheral.
23.14.1 Structure of Message Objects
Figure 23-17 shows the structure of a message object.
The grayed fields are those parts of the message object which are represented in dedicated registers. For
example, the transmit request flags of all message objects are represented in centralized transmit request
registers.
UMask Msk[28:0 MXtd
]
MsgVal ID[28:0] Xtd
Name Value
MsgVal
0
1
UMask
0
1
ID[28:0]
ID[28:0]
ID[28:18] 11-bit ("standard") identifier bits
Msk[28:0]
0
1
Xtd
0
1
SPRUHE8E – October 2012 – Revised November 2019
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Figure 23-17. Structure of a Message Object
Message Object
MDir EoB unused
Dir DLC[3:0] Data 0
Table 23-2. Message Object Field Descriptions
Description
Message valid
The message object is ignored by the message handler.
The message object is to be used by the message handler.
Note: This bit may be kept at level '1' even when the identifier bits ID[28:0], the control bits Xtd, Dir, or the
data length code DLC[3:0] are changed. It should be reset if the Messages Object is no longer required.
Use Acceptance Mask
Mask bits (Msk[28:0], MXtd and MDir) are ignored and not used for acceptance filtering.
Mask bits are used for acceptance filtering.
Note: If the UMask bit is set to one, the message object's mask bits have to be programmed during
initialization of the message object before MsgVal is set to one.
Message Identifier
29-bit ("extended") identifier bits
Identifier Mask
The corresponding bit in the message identifier is not used for acceptance filtering (don't care).
The corresponding bit in the message identifier is used for acceptance filtering.
Note: The bit functionality in the DCAN module is the opposite of the "Local Acceptance Mask" bit
functionality in the eCAN module found in older C28xx devices, where a "1" means the corresponding bit is
NOT used for filtering and "0" means it is used.
Extended Identifier
The 11-bit ("standard") identifier will be used for this message object.
The 29-bit ("extended") identifier will be used for this message object.
Copyright © 2012–2019, Texas Instruments Incorporated
NewDat MsgLst RxIE
Data 1 Data 2 Data 3
Message RAM
TxIE IntPnd RmtEn
Data 4 Data 5 Data 6
M3 Controller Area Network (CAN)
TxRqst
Data 7
1577