NXP Semiconductors MWCT101 S Series, Reference Manual

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49.5.11.4 Pretended Networking mode
This is a special low-power mode used to receive wakeup messages with low power
consumption. This mode can be selected to operate together with Stop mode. Before
entering one of these low-power modes, MCR [PNET_EN] must be asserted. After
entering the low-power mode, CHI subblock is shut down and CAN_PE subblock is kept
active, so that the Rx receive process is still active to filter incoming messages (see
Receive process under Pretended Networking mode ) as defined by the configuration
registers (see Pretended Networking Control 1 register (CTRL1_PN) ). Upon detecting a
wakeup event, a Wake Up interrupt is issued to the system.
To enter Pretended Networking mode, FlexCAN must be in normal mode (neither in
Freeze nor in Disable mode). Under Pretended Networking mode, FlexCAN keeps itself
synchronized with the CAN BUS in Stop mode. Then, when Stop mode is requested,
FlexCAN performs the following steps:
• Waits to be in Idle state, or else waits for the third bit of Intermission, and then
checks it to be recessive.
• Sets MCR[LPM_ACK].
• Requests the shutdown of the CHI submodule clock, while keeping the PE
submodule clock active.
FlexCAN can exit Pretended Networking mode by the following ways:
• The CPU removes the Stop Mode request.
• FlexCAN will wait until Bus Idle or third bit of Intermission state to negate
MCR[LPM_ACK].
The above exit ways can be triggered either by the FlexCAN action upon detecting a
wakeup event and issuing the respective interrupt, or by the CPU itself upon being waked
up by another method. In consequence, FlexCAN will wait until the Bus Idle state or
until the third bit of Intermission state to negate MCR[LPM_ACK] and resume Normal
mode. This procedure ensures that FlexCAN will be synchronized to the CAN bus after
exiting Pretended Networking mode. The CPU must wait for MCR[LPM_ACK] to be
negated before performing any access to FlexCAN.
NOTE
For more information about the difference between FD and
non-FD regarding this feature, see
Table 49-3 .
Functional description
MWCT101xS Series Reference Manual, Rev. 3, 07/2019
1708 NXP Semiconductors