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transfer is completed, the CAN controller issues a DMA peripheral request to perform the next message
object transfer. The request remains active until the first read or write to the message interface register.
Related Information
•
on page 16-1
•
Features of the System Manager
on page 14-1
Automatic Retransmission
The CAN controller provides a means for automatic retransmission of frames that have lost arbitration or
have errors during transmission. Retransmission happens automatically without user intervention or
notification. Normal confirmation is given when the transmission is successfully complete.
Test Mode
To enable test mode, set the test mode enable bit (
Test
) in the
CCTRL
register to 1. This action activates
write access to the CAN test register (
CTR
).
Silent Mode
The CAN controller is set in the silent mode by programming the silent mode (
Silent
) bit in the test
register (
CTR
) to 1. In silent mode, the CAN controller is able to receive valid data frames and valid remote
frames, but it holds the
CAN_TXD
pin high, sending no data to the CAN bus. The silent mode can be used
to analyze the traffic on a CAN bus without affecting it by the transmission of dominant bits (acknowledge
bits, error frames). In ISO 11898-1, the silent mode is called the
bus monitoring mode
.
Figure 25-2: CAN Core in Silent Mode
CAN Controller
CAN_TXD
CAN_RXD
CAN Core
TX
RX
V
cc
Loopback Mode
The CAN controller is set in loopback mode by programming the loopback mode (
LBack
) bit in the test
register (
CTR
) to 1. In loopback mode, the CAN controller treats its own transmitted messages as received
messages and stores them (if they pass acceptance filtering) to a receive buffer.
To be independent from external stimulation, the CAN controller ignores acknowledge errors in loopback
mode. In this mode, the CAN controller provides internal feedback from its transmit (TX) output to its
receive (RX) input. The actual value of the input pin is disregarded by the CAN controller.
CAN Controller Introduction
Altera Corporation
cv_54025
Automatic Retransmission
25-8
2013.12.30