MC9S12HZ256 Datasheet, PDF (378/692 Pages) Freescale Semiconductor, Inc – HCS12 Microcontrollers

Chapter 12 Freescale’s Scalable Controller Area Network (MSCANV2)
12.4.5 Modes of Operation
12.4.5.1 Normal Modes
The MSCAN module behaves as described within this specification in all normal system operation modes.
12.4.5.2 Special Modes
The MSCAN module behaves as described within this specification in all special system operation modes.
12.4.5.3 Emulation Modes
In all emulation modes, the MSCAN module behaves just like normal system operation modes as
described within this specification.
12.4.5.4 Listen-Only Mode
In an optional CAN bus monitoring mode (listen-only), the CAN node is able to receive valid data frames
and valid remote frames, but it sends only “recessive” bits on the CAN bus. In addition, it cannot start a
transmision. If the MAC sub-layer is required to send a “dominant” bit (ACK bit, overload flag, or active
error flag), the bit is rerouted internally so that the MAC sub-layer monitors this “dominant” bit, although
the CAN bus may remain in recessive state externally.
12.4.5.5 Security Modes
The MSCAN module has no security features.
12.4.6 Low-Power Options
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 12-37 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.
For all modes, an MSCAN wake-up interrupt can occur only if the MSCAN is in sleep mode (SLPRQ = 1
and SLPAK = 1), wake-up functionality is enabled (WUPE = 1), and the wake-up interrupt is enabled
(WUPIE = 1).
MC9S12HZ256 Data Sheet, Rev. 2.04
378
Freescale Semiconductor