mc9s12xs128 Freescale Semiconductor, Inc, mc9s12xs128 Datasheet - Page 342

• Manufacturer Part Number: mc9s12xs128
• Description: Hcs12 Microcontrollers 16-bit Automotive Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Freescale’s Scalable Controller Area Network (S12MSCANV3)
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
Figure
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.
11.4.5
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.
Table 11-38
modes is entered by the given settings on the CSWAI and SLPRQ/SLPAK bits.
342
11-45).
Low-Power Options
summarizes the combinations of MSCAN and CPU modes. A particular combination of
The CPU cannot clear INITRQ before initialization mode (INITRQ = 1 and
INITAK = 1) is active.
Bus Clock Domain
CPU
Init Request
INITAK
Flag
Figure 11-45. Initialization Request/Acknowledge Cycle
S12XS Family Reference Manual, Rev. 1.10
INITRQ
sync.
INITAK
NOTE
SYNC
SYNC
CAN Clock Domain
sync.
INITRQ
INITAK
INIT
Flag
Freescale Semiconductor