Diagnosis Functions And Special Operational Modes; Receive-Only Mode - NEC V850ES/F 3-L Series User Manual

32-bit single-chip microcontroller

Table of Contents

18.13 Diagnosis Functions and Special Operational

Figure 18-32

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.

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 VALID bit of the CnCTRL

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

transmitted from the CAN module to the CAN bus even when a CAN bus error

is detected while receiving a message frame. Since no transmission can be

issued from the CAN module, the transmission error counter the CnERC.TEC7

to CnERC.TEC0 bits are never updated. Therefore, a CAN module in the

receive-only mode does not enter the bus-off state.

User's Manual U18743EE1V2UM00

the recessive

CAN Controller (CAN)