
DocID13284 Rev 2
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UM0404
CAN modules
baudrate defined by the protocol standard. On the other hand, the CPU frequency can be
reduced down to 8 MHz: providing the CAN module directly with the CPU clock disabling the
prescaler factor, it is still possible to obtain the maximum CAN speed (1Mbaud).
After reset the prescaler is enabled, so CPU clock is divided by 2 and then provided to the
CAN modules: according to the system clock frequency, the application can disable the
prescaler to obtain the required baudrate.
Section 21.4: Clock Prescaling
for the description of register XMISC.
21.5
CAN module: functional overview
The C-CAN consists of the components (see
) CAN Core, Message RAM,
Message Handler, Control Registers, and Module Interface.
The CAN Core performs communication according to the CAN protocol version 2.0 part A
and B. The bitrate can be programmed to values up to 1 Mbit/s depending on the used
technology. For the connection to the physical layer additional external transceiver
hardware is required.
For communication on a CAN network, individual Message Objects are configured. The
Message Objects and Identifier Masks for acceptance filtering of received messages are
stored in the Message RAM.
All functions concerning the handling of messages are implemented in the Message
Handler. Those functions are the acceptance filtering, the transfer of messages between the
CAN Core and the Message RAM, and the handling of transmission requests as well as the
generation of the module interrupt.
The register set of the C-CAN can be accessed directly by the CPU via the module
interface. These registers are used to control/configure the CAN Core and the Message
Handler and to access the Message RAM.
The C-CAN implements the following features:
•
Supports CAN protocol version 2.0 part A and B
•
Bitrates up to 1 Mbit/s
•
32 Message Objects
•
Each Message Object has its own identifier mask
•
Programmable FIFO mode (concatenation of Message Objects)
•
Maskable interrupt
•
Disabled Automatic Retransmission mode for Time Triggered CAN applications
•
Programmable loop-back mode for self-test operation