CAN_TX
CAN_RX
Tx
Rx
CAN Core
•
•
=1
DCAN
Functional Description
23.3.8.2.1 Automatic Retransmission
According to the CAN Specification (ISO11898), the DCAN provides a mechanism to automatically
retransmit frames which have lost arbitration or have been disturbed by errors during transmission. The
frame transmission service will not be confirmed to the user before the transmission is successfully
completed.
By default, this automatic retransmission is enabled. It can be disabled by setting bit disable automatic
retransmission (DAR) in the CAN Control register. Further details to this mode are provided in
.
23.3.8.2.2 Auto-Bus-On
By default, after the DCAN has entered Bus-Off state, the CPU can start a Bus-Off-Recovery sequence by
resetting the Init bit. If this is not done, the module will stay in Bus-Off state.
The DCAN provides an automatic Auto-Bus-On feature which is enabled by bit ABO in the CAN control
register. If set, the DCAN will automatically start the Bus-Off-Recovery sequence. The sequence can be
delayed by a user-defined number of L3_SLOW_GCLK cycles which can be defined in the Auto-Bus-On
Time register (DCAN ABOTR).
NOTE:
If the DCAN goes to Bus-Off state due to a massive occurrence of CAN bus errors, it stops
all bus activities and automatically sets the Init bit. Once the Init bit has been reset by the
CPU or due to the Auto-Bus-On feature, the device will wait for 129 occurrences of bus Idle
(equal to 129 * 11 consecutive recessive bits) before resuming normal operation. At the end
of the Bus-Off recovery sequence, the error counters will be reset.
23.3.8.3 Test Modes
The DCAN module provides several test modes which are mainly intended for production tests or self test.
For all test modes, the Test bit in the CAN control register needs to be set to one. This enables write
access to the test register (DCAN TEST).
23.3.8.3.1 Silent Mode
The silent mode may be used to analyze the traffic on the CAN bus without affecting it by sending
dominant bits (e.g., acknowledge bit, overload flag, active error flag). The DCAN is still able to receive
valid data frames and valid remote frames, but it will not send any dominant bits. However, these are
internally routed to the CAN core.
shows the connection of signals CAN_TX and CAN_RX to the CAN core in silent mode. Silent
mode can be activated by setting the Silent bit in the Test register to one. In ISO 11898-1, the silent mode
is called the bus monitoring mode.
Figure 23-5. CAN Core in Silent Mode
3890
Controller Area Network (CAN)
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated