XC886/888CLM
Controller Area Network (MultiCAN) Controller
User’s Manual
15-33
V1.3, 2010-02
MultiCAN, V1.0
15.1.9
Message Object Functionality
This section describes the functionality of the Message Objects in the MultiCAN module.
15.1.9.1
Standard Message Object
A message object is selected as Standard Message Object when bit field
MOFCRn.MMC = 0000
B
. The Standard Message Object can transmit and receive CAN
frames according to the basic rules as 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.
15.1.9.2
Single Data Transfer Mode
Single data transfer mode is a useful feature in order to broadcast data over the CAN
bus without unintended doubling 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 content of the first message gets lost and is replaced with the content of
the new received message (indicated by MSGLST = 1).
In single data transfer mode (SDT = 1), 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, then 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.
15.1.9.3
Single Transmit Trial
If bit MOFCRn.STT is set, then the transmission request is cleared (TXRQ = 0) when the
frame content of the message object has 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.
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