Diagnosis Functions And Special Operational Modes; Receive-Only Mode - NEC V850E/Dx3 Preliminary User's Manual

CAN Controller (CAN)
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19.14 Diagnosis Functions and Special Operational
Modes
The CAN 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.

19.14.1 Receive-only mode

The 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 in the CAN module is changed until "valid reception" is detected, so
that the baud rates in the module match ("valid reception" means 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). The
event of valid reception is indicated by setting the CnCTRL.VALID bit (1).
Figure 19-31 CAN module terminal connection in receive-only mode
In the receive-only mode, no message frames can be transmitted from the
CAN module to the CAN bus. Transmit requests issued for message buffers
defined as transmit message buffers are held pending.
In the receive-only mode, the CAN transmission pin (CTXDn) in the CAN
module is fixed to the recessive level. Therefore, no active error flag can be
Preliminary User's Manual U17566EE1V2UM00
CAN macro
Tx
Fixed to
the recessive
level
CTXDn CRXDn
Chapter 19
Rx
733