Datasheet

767
32117D–AVR-01/12
AT32UC3C
The channel mode is not changed when the channel is disabled, i.e. the Fault Confinement Reg-
ister (CANFC) is not cleared. Therefore, if the channel was in error passive mode before being
disabled, it stays in error passive mode when re-enabled.
Figure 29-5. Enable and Disable Sequences
29.6.2.3 Overload frames
The CAN protocol allows nodes to send overload frames to provide extra delay between two
messages.
User can at any time request to send overload frames by writing the Overload Request bit (CAN-
CTRL.OVRQ) to one. A single overload frame will then be sent at the end of the next message.
When transission of the overload frame starts, CANSR.OVS is set and CANCTRL.OVRQ is
cleared. At this time, user can write CANCTRL.OVRQ to one again to send a second overload
frame at the end of the first one. The CAN protocol specifies that maximum two overload frames
can be sent.
Figure 29-6. Overload Frame Request
29.6.2.4 Errors and fault confinement
This section refers to chapter 6 (Error handling) and chapter 7 (Fault confinement) of the CAN
Specification.
There are 5 different error types which are not mutually exclusive. Error status can be read in the
Interrupt Status Register (CANISR). Error status bits are set by hardware and can only be
cleared by user.
When the channel enters bus off state, the Bus Off Status bit (CANISR.BOFF) is set. In this
state the channel can no longer communicate on the bus. The channel can leave bus off state if
it detects 128 occurrences of 11 consecutive recessive bits on the bus.
The Last Selected MOb Status field (CANISR.LSMOB) identifies the MOb that was selected
when the error occurred. For some error types, a MOb has not been selected yet when the error
occurs. In this case, CANISR.LSMOB returns NONE.
CANSR.CES
enable request
(user write)
CANCTRL.CEN
disable request
(user write)
data frameCAN bus bus idle data frame
overload frame 1data or remote frame overload frame 2
CAN bus
CANCTRL.OVRQ
CANSR.OVS
user write user write
data or remote frame