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134
CP3BT26
Figure 61.
Data Direction Bit Clear
Setting the DDIR bit will cause the direction of the data stor-
age to be reversed — the last byte received is stored at the
highest address and the first byte is stored at the lowest ad-
dress, as shown in Figure 62.
Figure 62.
Data Direction Bit Set
LO
The Listen Only bit can be used to configure
the CAN interface to behave only as a receiv-
er. This means:
•
Cannot transmit any message.
•
Cannot send a dominant ACK bit.
•
When errors are detected on the bus, the
CAN module will behave as in the error
passive mode.
Using this listen only function, the CAN inter-
face can be adjusted for connecting to an op-
erating network with unknown bus speed.
0 – Transmit/receive mode.
1 – Listen-only mode.
IGNACK
When the Ignore Acknowledge bit is set, the
CAN module does not expect to receive a
dominant ACK bit to indicate the validity of a
transmitted message. It will not send an error
frame when the transmitted frame is not ac-
knowledged by any other CAN node. This fea-
ture can be used in conjunction with the
LOOPBACK bit for stand-alone tests outside
of a CAN network.
0 – Normal mode.
1 – The CAN module does not expect to re-
ceive a dominant ACK bit to indicate the
validity of a transmitted message.
LOOPBACK
When the Loopback bit is set, all messages
sent by the CAN module can also be received
by a CAN module buffer with a matching buff-
er ID. However, the CAN module does not ac-
knowledge a message sent by itself.
Therefore, the CAN module will send an error
frame when no other device connected to the
bus has acknowledged the message.
0 – No loopback.
1 – Loopback enabled.
Storage of Data Bytes
in the Buffer Memory
Sequence of Data Bytes on the Bus
CRC
Data8
t
Data7
Data6
Data5
Data4
Data3
Data2
Data1
ID
Data2
Data1
0A
16
Data4
Data3
08
16
Data6
Data5
06
16
Data8
Data7
04
16
Data Bytes
ADDR Offset
DS045
Storage of Data Bytes
in the Buffer Memory
Sequence of Data Bytes on the Bus
CRC
Data8
t
Data7
Data6
Data5
Data4
Data3
Data2
Data1
ID
Data7
Data8
0A
16
Data5
Data6
08
16
Data3
Data4
06
16
Data1
Data2
04
16
Data Bytes
ADDR Offset
DS046