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remote frame in the message object, it will store the received data length code. The data bytes of the
message object will remain unchanged.
•
If the RxIE bit is set, the IntPnd bit will be set when a received remote frame is accepted and stored in
the message object.
23.10.5 Configuration of a FIFO Buffer
With the exception of the EoB bit, the configuration of receive objects belonging to a FIFO buffer is the
same as the configuration of a single receive object.
To concatenate multiple message objects to a FIFO buffer, the identifiers and masks (if used) of these
message objects have to be programmed to matching values. Due to the implicit priority of the message
objects, the message object with the lowest number will be the first message object of the FIFO buffer.
The EoB bit of all message objects of a FIFO buffer except the last one have to be programmed to zero.
The EoB bits of the last message object of a FIFO buffer is set to one, configuring it as the end of the
block.
23.11 Message Handling
When initialization is finished, the CAN module synchronizes itself to the traffic on the CAN bus. It does
acceptance filtering on received messages and stores those frames that are accepted into the designated
message objects. The application has to update the data of the messages to be transmitted and to enable
and request their transmission. The transmission is requested automatically when a matching remote
frame is received.
The application may read messages which are received and accepted. Messages that are not read before
the next messages is accepted for the same message object will be overwritten. Messages may be read
interrupt-driven or after polling of NewDat.
23.11.1 Message Handler Overview
The message handler state machine controls the data transfer between the Rx/Tx Shift register of the
CAN Core and the Message RAM. It performs the following tasks:
•
Data transfer from Message RAM to CAN Core (messages to be transmitted).
•
Data transfer from CAN Core to the Message RAM (received messages).
•
Data transfer from CAN Core to the Acceptance Filtering unit.
•
Scanning of Message RAM for a matching message object (acceptance filtering).
•
Scanning the same message object after being changed by IF1 or IF2 registers when priority is same
or higher as message the object found by last scanning.
•
Handling of TxRqst flags.
•
Handling of interrupt flags.
The message handler registers contains status flags of all message objects grouped into the following
topics:
•
Transmission request flags
•
New data flags
•
Interrupt pending flags
•
Message valid registers
Instead of collecting above listed status information of each message object via IFx registers separately,
these message handler registers provides a fast and easy way to get an overview e.g. about all pending
transmission requests.
All message handler registers are read-only.
SPRUH22I – April 2012 – Revised November 2019
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Copyright © 2012–2019, Texas Instruments Incorporated
Configuration of Message Objects
M3 Controller Area Network (CAN)
1525
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