Freescale Semiconductor Tower System Eval Kit for MC9S12GN32 TWR-S12GN32-KIT TWR-S12GN32-KIT Hoja De Datos

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Freescale Semiconductor

Due to independent clock domains within the MSCAN, INITRQ must be synchronized to all domains by
using a special handshake mechanism. This handshake causes additional synchronization delay (see

).

If there is no message transfer ongoing on the CAN bus, the minimum delay will be two additional bus
clocks and three additional CAN clocks. When all parts of the MSCAN are in initialization mode, the
INITAK flag is set. The application software must use INITAK as a handshake indication for the request
(INITRQ) to go into initialization mode.

The CPU cannot clear INITRQ before initialization mode (INITRQ = 1 and
INITAK = 1) is active.

If the MSCAN is disabled (CANE = 0), the MSCAN clocks are stopped for power saving.

If the MSCAN is enabled (CANE = 1), the MSCAN has two additional modes with reduced power
consumption, compared to normal mode: sleep and power down mode. In sleep mode, power consumption
is reduced by stopping all clocks except those to access the registers from the CPU side. In power down
mode, all clocks are stopped and no power is consumed.

 summarizes the combinations of MSCAN and CPU modes. A particular combination of

modes is entered by the given settings on the CSWAI and SLPRQ/SLPAK bits.