16.5 Message Objects
The eCAN module has 32 message objects (mailboxes).
Each message object can be configured to either transmit or receive. Each message object has its own
acceptance mask (in the eCAN mode; not in SCC mode).
A message object consists of a message mailbox with:
• The 29-bit message identifier
• The message control register
• 8 bytes of message data
• A 29-bit acceptance mask
• A 32-bit time stamp
• A 32-bit time-out value
Furthermore, corresponding control and status bits located in the registers allow control of the message objects.
16.6 Message Mailbox
The message mailboxes are the RAM area where the CAN messages are actually stored after they are received
or before they are transmitted.
The CPU may use the RAM area of the message mailboxes that are not used for storing messages as normal
memory.
Each mailbox contains:
• The message identifier
– 29 bits for extended identifier
– 11 bits for standard identifier
• The identifier extension bit, IDE (MSGID.31)
• The acceptance mask enable bit, AME (MSGID.30)
• The auto answer mode bit, AAM (MSGID.29)
• The transmit priority level, TPL (MSGCTRL.12-8)
• The remote transmission request bit, RTR (MSGCTRL.4)
• The data length code, DLC (MSGCTRL.3-0)
• Up to eight bytes for the data field
Each of the mailboxes can be configured as one of four message object types (see
). Transmit
and receive message objects are used for data exchange between one sender and multiple receivers (1
to n communication link), whereas request and reply message objects are used to set up a one-to-one
communication link.
Table 16-1. Message Object Behavior Configuration
Message Object Behavior
Mailbox Direction Register
(CANMD)
Auto-Answer Mode Bit (AAM)
Remote Transmission
Request Bit (RTR)
Transmit message object
0
0
0
Receive message object
1
0
0
Remote-Request message object
1
0
1
Auto-Reply message object
0
1
0
Controller Area Network (CAN)
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
1007
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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