Local Power-Down Mode
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SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
Controller Area Network (DCAN) Module
23.12 Local Power-Down Mode
Besides the centralized power down mechanism controlled by the PCR module (global power down, see
), the DCAN supports a local power-down mode that can be controlled within the DCAN
control registers.
23.12.1 Entering Local Power-Down Mode
The local power-down mode is requested by setting the PDR bit in CAN Control Register.
The DCAN then finishes all transmit requests of the message objects. When all requests are done, DCAN
waits until a bus idle state is recognized. Then it will automatically set the Init bit in CAN Control Register
to prevent any further CAN transfers, and it will also set the PDA bit in CAN Error and Status Register.
With setting the PDA bits, the DCAN module indicates that the local power-down mode has been entered.
During local power-down mode, the internal clocks of the DCAN module are turned off, but there is a wake
up logic (see
) that can be active, if enabled. Also the actual contents of the control
registers can be read back.
NOTE:
In local low power mode, the application should not clear the Init bit while PDR is set. If there
are any messages in the Message RAM configured as to be transmitted and the application
resets the init bit, these messages may be sent.
23.12.2 Wakeup From Local Power-Down Mode
There are two ways to wake up the DCAN from local power-down mode:
1. The application could wake up the DCAN module manually by clearing the PDR bit and then clearing
the Init bit in CAN Control Register.
2. Alternatively, a CAN bus activity detection circuit can be activated by setting the wake up on bus
activity bit (WUBA) in CAN Control Register. If this circuit is active, on occurrence of a dominant CAN
bus level, the DCAN will automatically start the wake up sequence. It will clear the PDR bit in CAN
Control Register and also clear the PDA bit in Error and Status Register. The WakeUpPnd bit in CAN
Error and Status Register will be set. If Status Interrupts are enabled, also an interrupt will be
generated. Finally the Init bit in CAN control register will be cleared.
After the Init bit has been cleared, the module waits until it detects 11 consecutive recessive bits on the
CAN_RX pin and then goes Bus-Active again.
NOTE:
The CAN transceiver circuit has to stay active while CAN bus observation. The first CAN
message, which initiates the bus activity, cannot be received. This means that the first
message received in power-down and automatic wake-up mode, is lost.
shows a flow diagram about entering and leaving local power-down mode.
