AT572D940HF_14 Datasheet, PDF (671/745 Pages) ATMEL Corporation – High Performance MagicV VLIW DSP

AT572D940HF Preliminary
An error active unit takes part in bus communication and sends an active error frame when the
CAN controller detects an error.
An error passive unit cannot send an active error frame. It takes part in bus communication, but
when an error is detected, a passive error frame is sent. Also, after a transmission, an error pas-
sive unit waits before initiating further transmission.
A bus off unit is not allowed to have any influence on the bus.
For fault confinement, two errors counters (TEC and REC) are implemented. These counters are
accessible via the CAN_ECR register. The state of the CAN controller is automatically updated
according to these counter values. If the CAN controller is in Error Active state, then the ERRA
bit is set in the CAN_SR register. The corresponding interrupt is pending while the interrupt is
not masked in the CAN_IMR register. If the CAN controller is in Error Passive Mode, then the
ERRP bit is set in the CAN_SR register and an interrupt remains pending while the ERRP bit is
set in the CAN_IMR register. If the CAN is in Bus-off Mode, then the BOFF bit is set in the
CAN_SR register. As for ERRP and ERRA, an interrupt is pending while the BOFF bit is set in
the CAN_IMR register.
When one of the error counters values exceeds 96, an increased error rate is indicated to the
controller through the WARN bit in CAN_SR register, but the node remains error active. The cor-
responding interrupt is pending while the interrupt is set in the CAN_IMR register.
Refer to the Bosch CAN specification v2.0 for details on fault confinement.
33.6.4.3
Overload
The overload frame is provided to request a delay of the next data or remote frame by the
receiver node (“Request overload frame”) or to signal certain error conditions (“Reactive over-
load frame”) related to the intermission field respectively.
Reactive overload frames are transmitted after detection of the following error conditions:
• Detection of a dominant bit during the first two bits of the intermission field
• Detection of a dominant bit in the last bit of EOF by a receiver, or detection of a dominant bit
by a receiver or a transmitter at the last bit of an error or overload frame delimiter
The CAN controller can generate a request overload frame automatically after each message
sent to one of the CAN controller mailboxes. This feature is enabled by setting the OVL bit in the
CAN_MR register.
Reactive overload frames are automatically handled by the CAN controller even if the OVL bit in
the CAN_MR register is not set. An overload flag is generated in the same way as an error flag,
but error counters do not increment.
33.6.5
Low-power Mode
In Low-power Mode, the CAN controller cannot send or receive messages. All mailboxes are
inactive.
In Low-power Mode, the SLEEP signal in the CAN_SR register is set; otherwise, the WAKEUP
signal in the CAN_SR register is set. These two fields are exclusive except after a CAN control-
ler reset (WAKEUP and SLEEP are stuck at 0 after a reset). After power-up reset, the Low-
power Mode is disabled and the WAKEUP bit is set in the CAN_SR register only after detection
of 11 consecutive recessive bits on the bus.
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