cp3cn23 National Semiconductor Corporation, cp3cn23 Datasheet - Page 83

• Manufacturer Part Number: cp3cn23
• Description: Cp3cn23 Reprogrammable Connectivity Processor With Dual Can Interfaces
• Manufacturer: National Semiconductor Corporation

17.2
This section provides a generic overview of the basic con-
cepts of the Controller Area Network (CAN).
The CAN protocol is a message-based protocol that allows
a total of 2032 (2
format and 512 million (2
extended frame format.
Every CAN Frame is broadcast on the common bus. Each
module receives every frame and filters out the frames
which are not required for the module's task. For example,
if a dashboard sends a request to switch on headlights, the
CAN module responsible for brake lights must not process
this message.
BASIC CAN CONCEPTS
11
- 16) different messages in the standard
29
- 16) different messages in the
CAN CORE
INTERFACE MANAGEMENT
Interface Management
Interface Management
Bit Stream Processor
Acceptance Filtering
CAN PRESCALER
Control
ACCEPTANCE
BTL CONFIG
CONTROL
Processor
Processor
MASKS
Figure 16. CAN Block Diagram
BTL, RX shift, TX shift, CRC
Status
CTX
Transceiver Logic
CPU BUS
Control
83
0
A CAN master module has the ability to set a specific bit
called the “remote data request bit” (RTR) in a frame. Such
a message is also called a “Remote Frame”. It causes an-
other module, either another master or a slave which ac-
cepts this remote frame, to transmit a data frame after the
remote frame has been completed.
Additional modules can be added to an existing network
without a configuration change. These modules can either
perform completely new functions requiring new data, or
process existing data to perform a new functionality.
As the CAN network is message oriented, a message can
be used as a variable which is automatically updated by the
controlling processor. If any module cannot process infor-
mation, it can send an overload frame.
RAM
CANnTX
1
Error Management Logic
Message Buffer 14
Message Buffer 0
Message Buffer 1
TX/RX
TX/RX
TX/RX
Data
0
CANnRX
1
DS281
Wake-Up
CRX
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