
CHAPTER 19 CAN CONTROLLER
Preliminary User’s Manual U16541EJ1V0UM
686
A CAN module in the “receive-only mode” is also not able to generate a dominant bit on the CAN bus in the ACK
slot of the ACK field upon a valid reception of a message frame. Furthermore, in “receive-only mode”, no overload
frames can be generated.
Caution
If only 2 CAN nodes are connected to the CAN bus and one of the CAN nodes is operating in
“receive-only mode”, there is no acknowledgment on the CAN bus. Due to the missing
acknowledgment, the transmitter will send an active error flag and repeat sending the message
frame.
The transmitter becomes error passive after sending the message frame 16 times
(assuming the error counters were zero in the beginning and no other errors have occurred).
When the message frame is sent for the 17th time, the transmitter generates a passive error flag,
so the transmitter in “receive-only mode” gets the first “valid” message frame and the VALID bit
is set (1) for the first time.
19.13.2 Single-shot mode
In the operational mode “single-shot mode” automatic re-transmission as defined in the CAN protocol is switched
off. (According to the CAN protocol, a message frame transmission that has been aborted by either ‘a(chǎn)rbitration loss’ or
‘error occurrence’ has to be repeated without any interaction by software.)
The “single-shot mode” disables the re-transmission of an aborted message frame transmission according the
setting of the AL bit in C0CTRL register. When the AL bit is cleared (0) re-transmission upon ‘a(chǎn)rbitration loss’ and
upon ‘error occurrence’ is disabled. If the AL bit is set (1), re-transmission upon ‘error occurrence’ is disabled, but re-
transmission upon ‘a(chǎn)rbitration loss’ is enabled. As a consequence, the TRQ flag in a message buffer defined as a
transmit message buffer may be cleared (0) by the following events.
Successful transmission of the message frame
‘Arbitration loss’ while sending the arbitration field of the message frame
‘Error occurrence’ while sending the message frame
The events ‘a(chǎn)rbitration loss’ and ‘error occurrence’ have to be distinguished by checking the LEC2 to LEC0 bits in
the C0INTS register.
Upon a successful transmission, the ‘transmit successful’ interrupt status bit CINTS0 in the C0INTS register is set
(1). In addition, an interrupt request signal will be generated, when it has been enabled by setting the CIE0 enable bit
in the C0IE register (1).
The “single-shot mode” can be used when emulating time-triggered communication methods (ex. TTCAN level 1).