cp3ub26 National Semiconductor Corporation, cp3ub26 Datasheet - Page 128

• Manufacturer Part Number: cp3ub26
• Description: Reprogrammable Connectivity Processor With Usb And Can Interfaces
• Manufacturer: National Semiconductor Corporation

www.national.com
Setting the DDIR bit will cause the direction of the data stor-
age to be reversed — the last byte received is stored at the
LO
The Listen Only bit can be used to configure
the CAN interface to behave only as a receiv-
er. This means:
•
•
•
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.
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.
Sequence of Data Bytes on the Bus
Sequence of Data Bytes on the Bus
ID
ID
Storage of Data Bytes
in the Buffer Memory
Storage of Data Bytes
in the Buffer Memory
Data1
Data1
Data2
Data2
Figure 51. Data Direction Bit Clear
Figure 52. Data Direction Bit Set
Data3
Data3
Data4
Data4
ADDR Offset
ADDR Offset
128
0A
08
06
04
0A
08
06
04
16
16
16
16
16
16
16
16
highest address and the first byte is stored at the lowest ad-
dress, as shown in Figure 52.
IGNACK
LOOPBACK
Data5
Data5
Data6
Data6
Data1
Data3
Data5
Data7
Data8
Data6
Data4
Data2
Data Bytes
Data Bytes
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-
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.
Data7
Data7
ceive a dominant ACK bit to indicate the
validity of a transmitted message.
Data2
Data4
Data6
Data8
Data7
Data5
Data3
Data1
Data8
Data8
a
message
CRC
CRC
DS046
DS045
t
t
sent
by
itself.