mcf51ac256a Freescale Semiconductor, Inc, mcf51ac256a Datasheet - Page 361

• Manufacturer Part Number: mcf51ac256a
• Description: Mcf51ac Flexis
• Manufacturer: Freescale Semiconductor, Inc

If sleep mode is active, the SLPRQ and SLPAK bits are set
use SLPAK as a handshake indication for the request (SLPRQ) to go into sleep mode.
When in sleep mode (SLPRQ = 1 and SLPAK = 1), the MSCAN stops its internal clocks. However, clocks
that allow register accesses from the CPU side continue to run.
If the MSCAN is in bus-off state, it stops counting the 128 occurrences of 11 consecutive recessive bits
due to the stopped clocks. The TXCAN pin remains in a recessive state. If RXF = 1, the message can be
read and RXF can be cleared. Shifting a new message into the foreground buffer of the receiver FIFO
(RxFG) does not take place while in sleep mode.
It is possible to access the transmit buffers and to clear the associated TXE flags. No message abort takes
place while in sleep mode.
If the WUPE bit in CANCLT0 is not asserted, the MSCAN will mask any activity it detects on CAN. The
RXCAN pin is therefore held internally in a recessive state. This locks the MSCAN in sleep mode
(Figure
The MSCAN is able to leave sleep mode (wake up) only when:
After wake-up, the MSCAN waits for 11 consecutive recessive bits to synchronize to the CAN bus. As a
consequence, if the MSCAN is woken-up by a CAN frame, this frame is not received.
The receive message buffers (RxFG and RxBG) contain messages if they were received before sleep mode
was entered. All pending actions will be executed upon wake-up; copying of RxBG into RxFG, message
aborts and message transmissions. If the MSCAN remains in bus-off state after sleep mode was exited, it
continues counting the 128 occurrences of 11 consecutive recessive bits.
Freescale Semiconductor
•
•
CAN bus activity occurs and WUPE = 1
or
the CPU clears the SLPRQ bit
15-44). WUPE must be set before entering sleep mode to take effect.
The application software must avoid setting up a transmission (by clearing
one or more TXEx flag(s)) and immediately request sleep mode (by setting
SLPRQ). Whether the MSCAN starts transmitting or goes into sleep mode
directly depends on the exact sequence of operations.
The CPU cannot clear the SLPRQ bit before sleep mode (SLPRQ = 1 and
SLPAK = 1) is active.
MCF51AC256 ColdFire Integrated Microcontroller Reference Manual, Rev. 5
NOTE
NOTE
(Figure
15-43). The application software must
Freescale’s Controller Area Network (MSCANV1)
15-45