Power Saving Modes; Can Sleep Mode - NEC V850ES/F 3-L Series User Manual

Chapter 18

18.11 Power Saving Modes

18.11.1 CAN sleep mode

(1)
Note
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The CAN sleep mode can be used to set the CAN Controller to stand-by mode
in order to reduce power consumption. The CAN module can enter the CAN
sleep mode from all operation modes. Release of the CAN sleep mode returns
the CAN module to exactly the same operation mode from which the CAN
sleep mode was entered.
In the CAN sleep mode, the CAN module does not transmit messages, even
when transmission requests are issued or pending.
Entering CAN sleep mode
The CPU issues a CAN sleep mode transition request by writing 01
PSMODE[1:0] bits of the CnCTRL register.
This transition request is acknowledged only under the following conditions.
1. The CAN module is already in one of the following operation modes
– Normal operation mode
– Normal operation mode with ABT
– Receive-only mode
– Single-shot mode
– Self-test mode
– CAN stop mode in all the above operation modes
2. The CAN bus state is bus idle (the 4th bit in the interframe space is reces-
sive).
If the CAN bus is fixed to dominant, the request for transition to the CAN
sleep mode is held pending. Also the transition from CAN stop mode to
CAN sleep mode is independent of the CAN bus state.
3. No transmission request is pending
If a sleep mode request is pending, and at the same time a message is
received in a message box, the sleep mode request is not cancelled, but is
executed right after message storage has been finished. This may result in
AFCAN being in sleep mode, while the CPU would execute the RX interrupt
routine. Therefore, the interrupt routine must check the access to the message
buffers as well as reception history list registers by using the MBON flag, if
sleep mode is used.
Similarly, if a sleep mode request is pending, and at the same time a message
is transmitted in a message box, the sleep mode request is not cancelled, but
is executed. This may result in CAN being in sleep mode, while the CPU would
execute the transmit interrupt routine. Therefore, the interrupt routine must
check the access to the message buffers as well as transmission history list
registers by using the MBON flag, if sleep mode is used.
If any one of the conditions mentioned above is not met, the CAN module will
operate as follows.
• If the CAN sleep mode is requested from the initialization mode, the CAN
sleep mode transition request is ignored and the CAN module remains in
the initialization mode.
• If the CAN bus state is not bus idle (i.e., the CAN bus state is either
transmitting or receiving) when the CAN sleep mode is requested in one of
User's Manual U18743EE1V2UM00
CAN Controller (CAN)
to the
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