National Semiconductor CP3BT26 User Manual page 134

Sequence of Data Bytes on the Bus
ID
Setting the DDIR bit will cause the direction of the data stor-
age to be reversed — the last byte received is stored at the
Sequence of Data Bytes on the Bus
ID
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.
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Data1 Data2 Data3 Data4
Storage of Data Bytes
in the Buffer Memory
Figure 61. Data Direction Bit Clear
Data1 Data2 Data3 Data4
Storage of Data Bytes
in the Buffer Memory
Figure 62. Data Direction Bit Set
Data5 Data6 Data7
ADDR Offset Data Bytes
0A Data1 Data2
16
08 Data3 Data4
16
06 Data5 Data6
16
04 Data7 Data8
16
highest address and the first byte is stored at the lowest ad-
dress, as shown in Figure 62.
Data5 Data6 Data7
ADDR Offset Data Bytes
0A Data8 Data7
16
08 Data6 Data5
16
06 Data4 Data3
16
04 Data2 Data1
16
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
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.
134
Data8 CRC
t
DS045
Data8 CRC
t
DS046
a message sent by itself.