Texas Instruments TMS320 2833 Series User Manual

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SPRUI07–March 2020
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Controller Area Network (CAN)
13.5 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.
13.6 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 Table 13-1). 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 13-2 lists the mailbox RAM layout.
Table 13-1. 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

Texas Instruments TMS320 2833 Series Specifications

General

Brand	Texas Instruments
Model	TMS320 2833 Series
Category	Controller
Language	English