Rainbow Electronics AT91CAP9S250A - Manual (Page 695)

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6264A–CAP–21-May-07
AT91CAP9S500A/AT91CAP9S250A
Figure 39-8. Enabling Low-power Mode
39.6.5.2 Disabling Low-power Mode
The CAN controller can be awake after detecting a CAN bus activity. Bus activity detection is
done by an external module that may be embedded in the chip. When it is notified of a CAN
bus activity, the software application disables Low-power Mode by programming the CAN
controller.
To disable Low-power Mode, the software application must:
– Enable the CAN Controller clock. This is done by programming the Power
Management Controller (PMC).
– Clear the LPM field in the CAN_MR register
The CAN controller synchronizes itself with the bus activity by checking for eleven consecutive
“recessive” bits. Once synchronized, the WAKEUP signal in the CAN_SR register is set.
Depending on the corresponding mask in the CAN_IMR register, an interrupt is generated
while WAKEUP is set. The SLEEP signal in the CAN_SR register is automatically cleared
once WAKEUP is set. WAKEUP signal is automatically cleared once SLEEP is set.
If no message is being sent on the bus, then the CAN controller is able to send a message
eleven bit times after disabling Low-power Mode.
If there is bus activity when Low-power mode is disabled, the CAN controller is synchronized
with the bus activity in the next interframe. The previous message is lost (see
Figure 39-9 ).
SLEEP
(CAN_SR)
MRDY
(CAN_MSR1)
LPM
(CAN_MR)
LPEN= 1
CAN BUS
MRDY
(CAN_MSR3)
Mailbox 1 Mailbox 3
Arbitration lost
WAKEUP
(CAN_SR)
0x0 CAN_TIM