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R01UH0336EJ0102 Rev.1.02
Page 1124 of 1538
Jul 17, 2014
V850E2/PG4-L
Section 20 CAN Controller (FCN)
20.11 Diagnosis Functions and Special Operating Modes
The FCN module provides a receive-only mode, single-shot mode, and self-
test mode to support CAN bus diagnosis functions or the operation of special
CAN communication methods.
20.11.1
Receive-only Mode
Receive-only mode is used to monitor receive messages without causing any
interference on the CAN bus and can be used for CAN bus analysis nodes.
For example, this mode can be used for automatic baud-rate detection. The
baud rate of the FCN module changes until “valid reception” is detected, so
that the baud rates in the module match (“valid reception” means that a
message frame has been received in the CAN protocol layer without
occurrence of an error and with an appropriate ACK between nodes connected
to the CAN bus). A valid reception does not require message frames to be
stored in a receive message buffer (data frames) or transmit message buffer
(remote frames). A valid reception event is indicated and confirmed by setting
FCNnCMCLCTL.FCNnCMCLVALF to 1.
Figure 20-10
FCN Module Pin Connection in Receive-only Mode
In receive-only mode, no message frames can be transmitted from the FCN
module to the CAN bus. Transmit requests issued to message buffers defined
as transmit message buffers are held pending.
In receive-only mode, the FCN transmission pin FCNnTX of the FCN module is
fixed to the recessive level. Therefore, no active error flag can be transmitted
from the FCN module to the CAN bus even when a CAN bus error is detected
while receiving a message frame. Since the FCN module cannot send data,
the transmission error counter the FCNnCMERCNT.TEC7 to
FCNnCMERCNT.TEC0 bits are never updated. Therefore, the FCN module in
receive-only mode does not enter the bus-off state.
Furthermore, in receive-only mode, ACK is not returned to the CAN bus upon
the valid reception of a message frame. Internally, the local node recognizes
that it has transmitted ACK. No overload frame can be transmitted to the CAN
bus.
CAN macro
Rx
Tx
FCNnTX
FCNnRX
Fixed to
the recessive
level