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TC1728
Controller Area Network Controller (MultiCAN)
20.3.11
Message Object Functionality
This chapter describes the functionality of the Message Objects in the MultiCAN module.
20.3.11.1 Standard Message Object
A message object is selected as standard message object when bit field
MOFCRn.MMC = 0000
(see
Page
20-88). The standard message object can transmit
B
and receive CAN frames according to the basic rules described in the previous sections.
Additional services such as Single Data Transfer Mode or Single Transmit Trial (see
following sections) are available and can be individually selected.
20.3.11.2 Single Data Transfer Mode
Single Data Transfer Mode is a useful feature in order to broadcast data over the CAN
bus without unintended duplication of information. Single Data Transfer Mode is selected
via bit MOFCRn.SDT.
Message Reception
When a received message stored in a message object is overwritten by a new received
message, the contents of the first message are lost and replaced with the contents of the
new received message (indicated by MSGLST = 1).
If SDT is set (Single Data Transfer Mode activated), bit MSGVAL of the message object
is automatically cleared by hardware after the storage of a received Data Frame. This
prevents the reception of further messages.
After the reception of a Remote Frame, bit MSGVAL is not automatically cleared.
Message Transmission
When a message object receives a series of multiple remote requests, it transmits
several Data Frames in response to the remote requests. If the data within the message
object has not been updated in the time between the transmissions, the same data can
be sent more than once on the CAN bus.
In Single Data Transfer Mode (SDT = 1), this is avoided because MSGVAL is
automatically cleared after the successful transmission of a Data Frame.
After the transmission of a Remote Frame, bit MSGVAL is not automatically cleared.
20.3.11.3 Single Transmit Trial
If the bit STT in the message object function register is set (STT = 1), the transmission
request is cleared (TXRQ = 0) when the frame contents of the message object have
been copied to the internal transmit buffer of the CAN node. Thus, the transmission of
the message object is not tried again when it fails due to CAN bus errors.
User's Manual
20-48
V1.0, 2011-12
MultiCAN, V2.24
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